Quality-of-life request. I tried making a script that accomplishes this, but my results were limited.
Minor Inconvenience: when I want to apply a UI color to a cel or layer on the timeline, I need to click at least 3 times on the respective Properties panel.
Possible Solution: Make the “add a UI color” to a cel or layer feature directly accessible on the Properties panel. I’ve included a demo of one possible UI solution, albeit one that removes the ability to fully customize the color.