how to fill color in a fixed area

Respected Author, I read your profile on the site and was highly impressed. I want to be a software engineer like you are. Sir, my question is that is it possible to fill color in a fixed area of a screen. I read many articles but examples are given to fill color in rectangle,circle and other objects. This is very important for my live project. Waiting for your reply... Sincerely yours, Abhas