How about

Toilets/
Planetary Systems/
Molecules/
Smiley Faces/
Mythical Creatures/
Optics/
Circuit Boards/

Oh how about bits, a CRT is laid out with a pixel color and the layout has to have
small dots only using red green and blue, I hope I am getting that point across.  Like
this:

I knew I was full of myself on that one.

Would be interesting to see what everyone can come up with.