It is likely some form of algae, I would recommend some inverts to help keep it undre control. If that second pic is the same stuff, (I relaly cant tell, kinda fuzzy, almost to zoomed in), if the second pic is smooth and gel like, I would say it may actually be a sponge almost
There are 4 things that are that color actually, 3 of them I have in my tank, all three I have are good..kinda...but 1 of them I dont like in the main tank :/
1 is Coraline, it is all the colors on the rocks, comes in like 50 differant colors at that.
1 is sponges, they come in afew diff colors, I have seen white, clear, red, blue, green, and black
1 is MAcro algae, it is actaully not an algae, it is cyanobacteria I believe? has soe good and bad properties, I am tryint o get rid of the last of it in my tank atm. I have seen red and black
1 is hair algae type, I have seen red and green, as far as I now....an annoying algae that has little to no benefit in a tank.