OK, I created a new user account and it has the same issue when opening the color picker, just a big black circle. Guess that means it's an OS problem. BTW, I'm using 10.9.5 and thanks Virtual1 for helping sort this out. Obviously not a damaged .plist so I am guessing it's a corrupted color picker.
I have a complete clone of my system on an external HD so I could copy that color picker and swap it with the current one and see if that works.
