The invisible block.

Invisible Blocks are invisible until you get near them, where they will fade into visibility. When you go far away, they will vanish again. Can be used for tricking people by hiding secret entrances and bridges. Inside the block is an eyeball that will observe the wheel's movements (in the game) or the mouse (in the editor select screen, only in the Coloraze: Spectrum editor).

In the original Coloraze, they act the same, except they only come in white and there is no moving eye.