Just off the top of my head idea, is use a transparent label, and output text to it instead of to the default output.

Also, I don't know how Mik's chat would cause a lot of lag for you - All it's really doing is setting the transparency colour to pink, then making the background of the output the same pink you set. You might not even need to use a separate window, as he did, and continually line it up - you should be able do the same thing with a single window.

Edit: Just tested the second above theory - apparently, the transparency is applied to everything below the output that's in the same window, so that won't work - But the first one is still do-able.