Tablet Pen Hotkey Issue
I have a Huion H610PRO and I noticed this issue today. I set one button to "Alt+Space" so I could rotate the canvas but I noticed that the current color would change unintentionally. I did some testing and it appears that when the button on the pen is released it releases the "Space" assignment first, so for a split second the "Alt" hotkey is assigned by itself, which is the "fast color picker". So if your brush has moved to a different color when you release the button it will choose that color. It's an easy fix just change the hotkey to something that doesn't overlap with another hotkey, but just wanted to share in case this happens to others. Beware of assigning overlapping hotkeys to pen buttons!
Re: Tablet Pen Hotkey Issue
"Fast color picker" must be triggered only with a pen click. Maybe you've bound "Fast pick color" on ALT?