how do i color desktop folders ( Catalina ) on mac book pro

You need to download an app - with folders included. When you have them, do a command + i for a get info window. click on the little icon in the top left corner with command + c to copy, then on your existing icon in a get info window and press command + v to paste. I don't know that I would use the site I've linked to - just wanted to give you an idea what there is. I'd search the app store.

NOTE: some folders cannot be changed, mostly system installed folders. You should be able to change the ones that you have created though.

I just did a search at the app store and there are plenty of choices - I searched for "folder icons". That is safer than using the link I had posted (which I am now removing).