Hey ya'll! So I'd like to make a cake with gray frosting. Here is my question...how?!?!

And then I'd like some dark black accents. I try to use my black coloring but it turns almost a violet. Any suggestions? I'm going to be making my cake soon, like this evening!

TIA!

well i'm definitely no professional but usually when my icing dries it darkens. so it looks violet until it dries. hth