Turn on more lights? Actually Apple has already thought of this problem, press control + option + command + 8.
Wow that was cool, but is there a purpose to it? It looks really cool, that's all I know.
As for it still being too bright, ummmm, I don't really think there is much you can do, try sitting farther away from the minitor, or rather pushing it farther away from you. Turning on a light in the room should help even out how bright the screen looks as well.
EDIT: Checked apple help, apprently it's for universal access. It says "Switch to White on Black". Although I don't know who would need to do that. Maybe color blindness, or something.