I recently gave a mini-course on regression trees. As I talked about the red region in the following figure:

one of the audience members said they had no clue what I was referring to. It turns out they were color blind and could not identify the red region. Yikes!

Here is a colorblind friendly pallette courtesy of Cookbook for R

cbbPalette <- c("#000000", "#E69F00", "#56B4E9", "#009E73", "#F0E442", "#0072B2", "#D55E00", "#CC79A7")