I posted it in march, and it's not an april fools joke or anything. Skeleton, and it's predacessor Skeleton+ are First person Shooters. They're not 3D in the scense of polygons or anything. It's just a still image of a tunnel that gives a 3D perspective. You can move through it AD&D style, one screen forward at a time.

It's really an awesome game for 2600. it wouldn't be impressive on any other game, but it was great for 2600

Technically, the Atari has a color palate of 128 colors, and it can show them all at once. But it's limited to 7 colors per scan line, without flicker. 2 BG colors, 2 Sprite colors, 2 Missile colors, and one ball color. That's why most games are limited to just a handful of colors, they use the same colors from scanline to scanline.