Several different colors of algae on substrate. What is it?

[RussC]

Algae comes and goes. But there are some interesting colors? Some will stay longer than others. Its not a problem. And it only seems to be on my substrate. If its on my rocks I can't see it. What is all of it? I've been through the brown diatome phase. Some of it looks similar. But by no means is it a problem. Some is red/pupleish. Some even looks green.

 

[nereefpat]

Impossible to tell without a picture, but probably cyanobacteria. It comes in many colors, from red to green.