How do I set default background color in Textedit?
Preferences -> New Document -> Font doesnt help.
That black on white isn't too good in nights.
Press command + T, you should see this window.
Another solution to your problem might simply be to invert your colors, you can toggle that by doing control + option + command + 8
You could also use WriteRoom. It's based on TextEdit but has a few additional features like customizable themes.