Re: Watercolors saturation simulation
Yep, "BUILD UP" refers to the speed or amount of material the brush deposits on the canvas. I deliberately didn't do brush loading and draining, because I deliberately didn't do a "simulation" of real life painting. This is a virtual environment where the magic never stops! 
However, I do see the benefit of such natural behavior and will likely make something like it possible eventually, but only as an extra option.

However, I do see the benefit of such natural behavior and will likely make something like it possible eventually, but only as an extra option.