OS X: accidentally switched my desktop to "white on black"

It took me quite a while to find the right group of system preferences, where to switch it back to "black on white": Universal Access.

Apple Universal Access is a component of the Mac OS X operating system that provides computing abilities to the blind, deaf, and handicapped.

Update 2012-10-01
It happened again (in a rather uncomfortable situation), and it took me a little to get here and read this. Success.
I don't want it to happen again, and I switch off all these Universal Access keyboard shortcuts.