Yellowish Orengy Stuff?

[corpse fish]

I have a 3 week old (about) 7.5 gal. tank and on the rocks in there, there is like this yellow-orange stuff that has the same kind of like patterns of algae. Any ideas on what it is?

 

[Tokis-Phoenix]

What types of rocks do you have in there do you know? Many types of rocks contain metal ores, its quite posible they are rusting in the tank.