Suggestion: Variable Alpha transparency for the background of the chat window when maximized.
Reason:
When playing the game today I notice that chatting with the chat window maximized (while mining especially) was difficult because the background of the chat window is so transparent, that whatever is going on in the background tends to over power the text in the chat window.

you could skin it yourself :P

Spidey's right -- the main chatbox area is part of the area that users can skin and make more/less opaque. There are many good skins out there that might do what you want -- go try them out.