Default colorscheme to something besides green <--> red

[nelsonauner]

I absolutely love this project, unfortunately, the default colorscheme is really hard to read for me and the 8% of men who are red/green colorblind (I know, cue the world's tiniest violin 🎻 )

@jdechalendar would you be OK if I created a PR to either:

1. Change the default colorscheme to a single hue (light to dark)
2. If you really want two colors, change to blue <--> red
3. If you really want green<--> red, I could add an option to pick another colorscheme

I would prefer (1) or (2) because it's easier for me to code, and then also screenshots of this tool get shared

A quick reference: https://www.datylon.com/blog/data-visualization-for-colorblind-readers#good-bad-charts