I cannot change the color of the presets as I was doing before. The color dialog works ok but the selected color doesn't update in BTT.
I am on 5.285 alpha on a M2 Max, sequoia 15.3.2 and a clean configuration
Seems to work fine here, does your color update when you restart BTT?
No.
Am I doing it right? I click the preset menu and the presets window appears. Then click on a preset color, color window appears, I change the color and inmmeditely the preset window closes. When I reopen the presets window the original color persists.
Arghh! this tiny bug.... I have discovered now that it only occurs when using the mouse with mouse app BetterMouse.
If I use the trackpad or close BetterMouse, the problem disappears. However, I’ve only encountered the bug when using BetterTouchTool. In other apps, the color picker works ok. 
weird, but at least that explains why nobody else has reported this. I‘ll check whether I can reproduce it with BetterMouse
It is the BetterMouse "click through" interfering. Disabling the "Left click-though" option in Buttons section, makes color picker work again