There's no magic bullet for finding where a color is used. You'll need to cycle through the page items on your layer of interest, looking at all the properties of every object that has properties with "Color" in their names. When the page item is a text frame, you'll need to check its text -- I think you can work with textStyleRanges to do that, but maybe not because they don't catch things like nested and grep styles.
What do you want to do when you find a color in use on your layer?
It will undoubtedly make a script like this run faster if you do the homework and develop lists of the specific properties of interest rather than hunt through every possible property for the word "Color" dynamically.
Dave
![[Jongware]](/people/%5BJongware%5D/avatar/30.png?a=20686){kind=small}