diff --git a/internal/app/model.go b/internal/app/model.go
index 224dffd..9b0fd07 100644
--- a/internal/app/model.go
+++ b/internal/app/model.go
@@ -156,6 +156,7 @@ func NewModel() (Model, error) {
 	store := comments.NewStore(gitDir)
 	loadedComments, loadErr := store.Load()
 	appConfig, configPath, configErr := config.Load()
+	diffview.InitializeTheme(appConfig.Theme)
 	if appConfig.LeaderCommands == nil {
 		appConfig.LeaderCommands = make(map[string]string)
 	}
diff --git a/internal/config/config.go b/internal/config/config.go
index 48eb15a..bc13339 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -15,6 +15,7 @@ const (
 
 type AppConfig struct {
 	LeaderCommands map[string]string `json:"leader_commands"`
+	Theme          string            `json:"theme,omitempty"`
 }
 
 func Load() (AppConfig, string, error) {
@@ -29,6 +30,7 @@ func Load() (AppConfig, string, error) {
 func LoadFromPath(path string) (AppConfig, error) {
 	cfg := AppConfig{
 		LeaderCommands: make(map[string]string),
+		Theme:          "auto",
 	}
 
 	data, err := os.ReadFile(path)
@@ -51,6 +53,12 @@ func LoadFromPath(path string) (AppConfig, error) {
 		cfg.LeaderCommands = make(map[string]string)
 	}
 
+	theme, err := normalizeTheme(cfg.Theme)
+	if err != nil {
+		return AppConfig{}, err
+	}
+	cfg.Theme = theme
+
 	normalized := make(map[string]string, len(cfg.LeaderCommands))
 	for k, v := range cfg.LeaderCommands {
 		key := strings.TrimSpace(k)
@@ -71,6 +79,19 @@ func LoadFromPath(path string) (AppConfig, error) {
 	return cfg, nil
 }
 
+func normalizeTheme(raw string) (string, error) {
+	theme := strings.ToLower(strings.TrimSpace(raw))
+	if theme == "" {
+		return "auto", nil
+	}
+	switch theme {
+	case "auto", "light", "dark":
+		return theme, nil
+	default:
+		return "", fmt.Errorf("theme %q must be one of auto, light, dark", raw)
+	}
+}
+
 func DefaultPath() (string, error) {
 	home, err := configHome()
 	if err != nil {
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index 8a8e416..c6f2911 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -15,6 +15,9 @@ func TestLoadFromPathMissingFile(t *testing.T) {
 	if len(cfg.LeaderCommands) != 0 {
 		t.Fatalf("expected empty commands, got %d", len(cfg.LeaderCommands))
 	}
+	if cfg.Theme != "auto" {
+		t.Fatalf("expected default theme auto, got %q", cfg.Theme)
+	}
 }
 
 func TestLoadFromPathParsesLeaderCommands(t *testing.T) {
@@ -36,6 +39,22 @@ func TestLoadFromPathParsesLeaderCommands(t *testing.T) {
 	}
 }
 
+func TestLoadFromPathParsesTheme(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "config.json")
+	if err := os.WriteFile(path, []byte(`{"theme":"LiGhT"}`), 0o644); err != nil {
+		t.Fatalf("WriteFile() error = %v", err)
+	}
+
+	cfg, err := LoadFromPath(path)
+	if err != nil {
+		t.Fatalf("LoadFromPath() error = %v", err)
+	}
+	if cfg.Theme != "light" {
+		t.Fatalf("expected light theme, got %q", cfg.Theme)
+	}
+}
+
 func TestLoadFromPathRejectsInvalidKey(t *testing.T) {
 	dir := t.TempDir()
 	path := filepath.Join(dir, "config.json")
@@ -48,6 +67,18 @@ func TestLoadFromPathRejectsInvalidKey(t *testing.T) {
 	}
 }
 
+func TestLoadFromPathRejectsInvalidTheme(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "config.json")
+	if err := os.WriteFile(path, []byte(`{"theme":"sepia"}`), 0o644); err != nil {
+		t.Fatalf("WriteFile() error = %v", err)
+	}
+
+	if _, err := LoadFromPath(path); err == nil {
+		t.Fatalf("expected error for invalid theme")
+	}
+}
+
 func TestDefaultPathUsesXDGConfigHome(t *testing.T) {
 	xdg := t.TempDir()
 	t.Setenv("XDG_CONFIG_HOME", xdg)
diff --git a/internal/diffview/render.go b/internal/diffview/render.go
index b2fed27..b6f0c38 100644
--- a/internal/diffview/render.go
+++ b/internal/diffview/render.go
@@ -83,6 +83,15 @@ var (
 
 	commentInlineTextStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("250")).Background(lipgloss.Color("236"))
 
+	syntaxKeywordColor      = lipgloss.Color("141")
+	syntaxStringColor       = lipgloss.Color("186")
+	syntaxCommentColor      = lipgloss.Color("244")
+	syntaxTypeColor         = lipgloss.Color("117")
+	syntaxFunctionColor     = lipgloss.Color("221")
+	syntaxNumberColor       = lipgloss.Color("215")
+	syntaxOperatorColor     = lipgloss.Color("204")
+	syntaxPreprocessorColor = lipgloss.Color("178")
+
 	syntaxLexerCacheMu sync.RWMutex
 	syntaxLexerCache   = make(map[string]chroma.Lexer)
 )
@@ -456,21 +465,21 @@ func styleStateAt(pos int, ranges []textRange, syntax []syntaxRange, rangeIdx, s
 func applySyntaxClass(base lipgloss.Style, class syntaxClass) lipgloss.Style {
 	switch class {
 	case syntaxClassKeyword:
-		return base.Foreground(lipgloss.Color("141"))
+		return base.Foreground(syntaxKeywordColor)
 	case syntaxClassString:
-		return base.Foreground(lipgloss.Color("186"))
+		return base.Foreground(syntaxStringColor)
 	case syntaxClassComment:
-		return base.Foreground(lipgloss.Color("244")).Italic(true)
+		return base.Foreground(syntaxCommentColor).Italic(true)
 	case syntaxClassType:
-		return base.Foreground(lipgloss.Color("117"))
+		return base.Foreground(syntaxTypeColor)
 	case syntaxClassFunction:
-		return base.Foreground(lipgloss.Color("221"))
+		return base.Foreground(syntaxFunctionColor)
 	case syntaxClassNumber:
-		return base.Foreground(lipgloss.Color("215"))
+		return base.Foreground(syntaxNumberColor)
 	case syntaxClassOperator:
-		return base.Foreground(lipgloss.Color("204"))
+		return base.Foreground(syntaxOperatorColor)
 	case syntaxClassPreprocessor:
-		return base.Foreground(lipgloss.Color("178"))
+		return base.Foreground(syntaxPreprocessorColor)
 	default:
 		return base
 	}
diff --git a/internal/diffview/theme.go b/internal/diffview/theme.go
new file mode 100644
index 0000000..e41abcd
--- /dev/null
+++ b/internal/diffview/theme.go
@@ -0,0 +1,160 @@
+package diffview
+
+import (
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/charmbracelet/lipgloss"
+	"github.com/muesli/termenv"
+)
+
+// InitializeTheme configures diff colors from one of: auto, dark, light.
+func InitializeTheme(mode string) {
+	theme := strings.ToLower(strings.TrimSpace(mode))
+	if theme == "" {
+		theme = "auto"
+	}
+
+	dark := true
+	switch theme {
+	case "dark":
+		dark = true
+	case "light":
+		dark = false
+	default:
+		dark = detectDarkBackground()
+	}
+
+	if dark {
+		applyDarkTheme()
+		return
+	}
+	applyLightTheme()
+}
+
+func detectDarkBackground() bool {
+	if dark, ok := darkFromColorFGBG(os.Getenv("COLORFGBG")); ok {
+		return dark
+	}
+	return termenv.HasDarkBackground()
+}
+
+func darkFromColorFGBG(value string) (bool, bool) {
+	parts := strings.Split(strings.TrimSpace(value), ";")
+	for i := len(parts) - 1; i >= 0; i-- {
+		idx, err := strconv.Atoi(strings.TrimSpace(parts[i]))
+		if err != nil {
+			continue
+		}
+		return isDarkColorIndex(idx), true
+	}
+	return false, false
+}
+
+func isDarkColorIndex(idx int) bool {
+	if idx < 0 {
+		return true
+	}
+	if idx <= 6 {
+		return true
+	}
+	if idx <= 15 {
+		return false
+	}
+	if idx >= 16 && idx <= 231 {
+		cube := idx - 16
+		r := cube / 36
+		g := (cube / 6) % 6
+		b := cube % 6
+		return rgbLuma(cubeChannelValue(r), cubeChannelValue(g), cubeChannelValue(b)) < 128
+	}
+	if idx >= 232 && idx <= 255 {
+		gray := 8 + (idx-232)*10
+		return gray < 128
+	}
+	return idx < 128
+}
+
+func cubeChannelValue(v int) int {
+	if v <= 0 {
+		return 0
+	}
+	return 55 + v*40
+}
+
+func rgbLuma(r, g, b int) int {
+	return (299*r + 587*g + 114*b) / 1000
+}
+
+func applyDarkTheme() {
+	addBaseStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("78")).Background(lipgloss.Color("#1a2620"))
+	deleteBaseStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("203")).Background(lipgloss.Color("#2a1f21"))
+	changeOldBaseStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("210")).Background(lipgloss.Color("#252022"))
+	changeNewBaseStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("121")).Background(lipgloss.Color("#1f2523"))
+	contextBaseStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("252"))
+	hunkBaseStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("111")).Bold(true)
+
+	addWordStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("121")).Background(lipgloss.Color("22")).Bold(true)
+	deleteWordStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("210")).Background(lipgloss.Color("52")).Bold(true)
+	cursorRowBg = lipgloss.Color("236")
+
+	cursorGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("16")).Background(lipgloss.Color("45")).Bold(true)
+	commentGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("16")).Background(lipgloss.Color("220")).Bold(true)
+	cursorCommentGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("16")).Background(lipgloss.Color("201")).Bold(true)
+	addGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("121")).Background(lipgloss.Color("22")).Bold(true)
+	deleteGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("210")).Background(lipgloss.Color("52")).Bold(true)
+	changeOldGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("210")).Background(lipgloss.Color("53")).Bold(true)
+	changeNewGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("121")).Background(lipgloss.Color("23")).Bold(true)
+	addMetaStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("121")).Background(lipgloss.Color("22")).Bold(true)
+	deleteMetaStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("210")).Background(lipgloss.Color("52")).Bold(true)
+	changeOldMetaStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("210")).Background(lipgloss.Color("53")).Bold(true)
+	changeNewMetaStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("121")).Background(lipgloss.Color("23")).Bold(true)
+
+	commentInlineTextStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("250")).Background(lipgloss.Color("236"))
+
+	syntaxKeywordColor = lipgloss.Color("141")
+	syntaxStringColor = lipgloss.Color("186")
+	syntaxCommentColor = lipgloss.Color("244")
+	syntaxTypeColor = lipgloss.Color("117")
+	syntaxFunctionColor = lipgloss.Color("221")
+	syntaxNumberColor = lipgloss.Color("215")
+	syntaxOperatorColor = lipgloss.Color("204")
+	syntaxPreprocessorColor = lipgloss.Color("178")
+}
+
+func applyLightTheme() {
+	addBaseStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("22")).Background(lipgloss.Color("194"))
+	deleteBaseStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("88")).Background(lipgloss.Color("224"))
+	changeOldBaseStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("130")).Background(lipgloss.Color("223"))
+	changeNewBaseStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("28")).Background(lipgloss.Color("193"))
+	contextBaseStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("236"))
+	hunkBaseStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("25")).Bold(true)
+
+	addWordStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("22")).Background(lipgloss.Color("121")).Bold(true)
+	deleteWordStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("88")).Background(lipgloss.Color("217")).Bold(true)
+	cursorRowBg = lipgloss.Color("254")
+
+	cursorGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("255")).Background(lipgloss.Color("25")).Bold(true)
+	commentGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("16")).Background(lipgloss.Color("220")).Bold(true)
+	cursorCommentGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("255")).Background(lipgloss.Color("161")).Bold(true)
+	addGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("22")).Background(lipgloss.Color("121")).Bold(true)
+	deleteGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("88")).Background(lipgloss.Color("217")).Bold(true)
+	changeOldGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("130")).Background(lipgloss.Color("223")).Bold(true)
+	changeNewGutterStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("28")).Background(lipgloss.Color("193")).Bold(true)
+	addMetaStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("22")).Background(lipgloss.Color("121")).Bold(true)
+	deleteMetaStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("88")).Background(lipgloss.Color("217")).Bold(true)
+	changeOldMetaStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("130")).Background(lipgloss.Color("223")).Bold(true)
+	changeNewMetaStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("28")).Background(lipgloss.Color("193")).Bold(true)
+
+	commentInlineTextStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("238")).Background(lipgloss.Color("253"))
+
+	syntaxKeywordColor = lipgloss.Color("55")
+	syntaxStringColor = lipgloss.Color("94")
+	syntaxCommentColor = lipgloss.Color("244")
+	syntaxTypeColor = lipgloss.Color("24")
+	syntaxFunctionColor = lipgloss.Color("130")
+	syntaxNumberColor = lipgloss.Color("88")
+	syntaxOperatorColor = lipgloss.Color("161")
+	syntaxPreprocessorColor = lipgloss.Color("89")
+}
diff --git a/internal/diffview/theme_test.go b/internal/diffview/theme_test.go
new file mode 100644
index 0000000..31f7927
--- /dev/null
+++ b/internal/diffview/theme_test.go
@@ -0,0 +1,48 @@
+package diffview
+
+import (
+	"testing"
+
+	"github.com/charmbracelet/lipgloss"
+)
+
+func TestDarkFromColorFGBG(t *testing.T) {
+	tests := []struct {
+		name  string
+		value string
+		dark  bool
+		ok    bool
+	}{
+		{name: "dark background", value: "15;0", dark: true, ok: true},
+		{name: "light background", value: "0;15", dark: false, ok: true},
+		{name: "with extra fields", value: "0;15;0", dark: true, ok: true},
+		{name: "empty", value: "", dark: false, ok: false},
+		{name: "non numeric", value: "foo;bar", dark: false, ok: false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			dark, ok := darkFromColorFGBG(tt.value)
+			if ok != tt.ok {
+				t.Fatalf("darkFromColorFGBG(%q) ok=%v want %v", tt.value, ok, tt.ok)
+			}
+			if dark != tt.dark {
+				t.Fatalf("darkFromColorFGBG(%q) dark=%v want %v", tt.value, dark, tt.dark)
+			}
+		})
+	}
+}
+
+func TestInitializeThemeExplicitModes(t *testing.T) {
+	defer applyDarkTheme()
+
+	InitializeTheme("light")
+	if cursorRowBg != lipgloss.Color("254") {
+		t.Fatalf("light theme did not set expected cursor row color")
+	}
+
+	InitializeTheme("dark")
+	if cursorRowBg != lipgloss.Color("236") {
+		t.Fatalf("dark theme did not set expected cursor row color")
+	}
+}