Is food coloring reef safe?

I got one of those DIY live rock kits from one of our meetings and before I mix it up I wanna try to give it some color. That’s the only thing I can think of to give it color that could be safe for the tank. Any ideas?

I can’t think of any reason it wouldn’t be. Of course it doesn’t take long for home made rock to color up once its in the tank so it may not be worth the risk of finding out I’m wrong.