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.
You could also use WriteRoom. It's based on TextEdit but has a few additional features like customizable themes.
While Louis told you the literal way to change your font and background color, the cursor will remain unchanged, making the editor practically unusable. That's just the Apple way.
Your best bet is to switch to another editor (like in Lauri's response) or simply tint your background to something less glaring than hard-white.
I know this ain't the answer you're looking for, but this is a computer for people who do NOT want the complexity of customization. Sorry.
Use TextMate.
You get all the simplicity of TexEdit (and you can easily disable all the little noise). I even find its startup speed better than TextEdit's.