One thing I loved a lot about old old artstudio was having two colors that you can switch on double tap. That made temporarily saving colors much more streamlined if I didn't want to save it to my swatches panel (which is even more clicks from the color picker in this new update...)
Is that something that can be possibly brought back? At the moment I'm working around that by locking transparency and using the eraser as a second brush tool with a second color, but it gets troublesome for me to unlock, change erase brush, erase, change erase brush back to my drawing brush, and re-lock layer transparency.