[ofalkaed]

>The aliens change colors when they descend to a new level (whoops).

That is how Space Invaders originally worked, used strips of colored cellophane to give the B&W graphics color and the aliens moved behind a different colored strip on each level down. So, maybe not an whoops?

Edit: After some reading, I guess it was the second release of Space Invaders which had the aliens change color as they dropped, first version only used the cellophane for a couple parts of the screen.