Refine color wheel hue spectrum a little more to get better color harmonies. The main issue is this: For many values of the hue slider, the triadic palette corresponds properly with the values on an artist's color wheel. Except for a set of secondary colors where the ArtColor's wheel lags a bit. If you set the hue to about 72 degrees, it shows what you should rather see at 90 degrees. Boo.
Calculate more exact inverse function for RGB-to-RYB. I.e., take the trilinear interpolation formulae, work them out into algebraic equations, invert them, and get direct formulae for both the RYB-to-RGB and its inverse.
Ditch the default RayGUI single-pixel font for text display and get a real font. Raylib supports nice fonts, after all. The single-pixel font works well for small text, but scales badly at medium sizes and is not very legible.
Make a help file Add facility for choosing Colorblind-friendly palettes.
There's some functions I have commented out but work fine, like an alternative rectangular color picker. Go ahead and play with them (if you can find a place for them on the screen!)
Screen shot button works correctly now.