Not the parent but speaking for myself. I read Lisp code by looking at the indentations. Parens don't matter unless they're wrong, and they're rarely wrong because my editor matches them as I type, and then I just tell it to indent everything properly. If the indentation looks goofy after that step I notice it immediately and only then do I look for paren problems.

Lisp is by far my favorite language but if I had to write it with a "dumb" text editor it would quickly stop being my favorite. Most editors are smart these days, and this is why it's hard to explain to newbies that the parens don't get in your way: When you build lisp code your editor manages the parens for you and they become essentially invisible. So color solves a problem that doesn't exist (for me).

Probably because you get used to them and different colours become distracting. Highlighting of active parentheses is more useful

Too much visual clutter with very little actual benefit. I found that I don't need/want to find matching parentheses by a mix of position AND color.