diff --git a/fullcontrol/visualize/point.py b/fullcontrol/visualize/point.py
index d32d1c8..0b4e4cd 100644
--- a/fullcontrol/visualize/point.py
+++ b/fullcontrol/visualize/point.py
@@ -75,9 +75,11 @@ def random_blue():
 
         def z_gradient(point: Point, bounding_box: BoundingBox):
             z_range = max(bounding_box.rangez, 0.00000001)
-            # round to the same number of decimal places used for xyz ('precision_xyz') to avoid numerical rounding errors causing negative or very large (not allowbale) values in plot_data
+            # round to the same number of decimal places used for xyz ('precision_xyz') to avoid numerical rounding errors causing negative or very large (not allowable) values in plot_data
             z_min = round(bounding_box.minz, 3)
-            return [0, round((point.z-z_min)/z_range, precision_color), 1]
+            # handle case where point.z is None (first point after extruder toggle)
+            z_val = point.z if point.z is not None else z_min
+            return [0, round((z_val-z_min)/z_range, precision_color), 1]
 
         def print_sequence(point_count_now: int, point_count_total: int):
             return [round(0.8*max(1-(2*point_count_now/point_count_total), 0), precision_color), round(max((2*point_count_now/point_count_total)-1, 0), precision_color), 1]