You can change the AT chat theme! What you need to do is right click the chat window, and click on "Inspect Element". Click on each piece of code, and look on "Matched CSS Rules". If it has a block of a color, with "rgb" by it, click on the color, and you can change it. Keep on experimenting with this till you have the perfect theme!
Q: Is this permanent?
Q: Is this illegal?
A: Nope. Because this does not affect anybody else in the chat, it is not illegal.
Q: Could this be done on Firefox?
A: Yes, but there might be different instructions.