Most Terminal apps come with a set of colour customisation options, but they can be difficult to tweak yourself. If you want to make your own, Terminal Sexy is a web app that makes it simple.
With Terminal Sexy you can easily pick colours and change the look of your Terminal app with a colour slider. You can also browse other people's colour schemes, import themes and share your own. The themes will work in any Terminal app that supports them, including XResources, Termite and iTerm 2.