Thanks Julie. I did try adding red/pink, but that gave me a red-purple, more like a magenta. I'm looking for a deep blue-purple. I wish I could be more specific, but I don't have Pantone numbers here. It's frustrating because I've mixed paint colors for years. I know how to mix color, but I can't seem to find the icing colors that will let me easily do it.
What about adding a touch of black? I would think that would work to "deepen", but, again, it's a bit hard to guide without seeing the color you have in mind. Concentrated liqua-gels, like AmeriColor and Chefmaster, can definitely give a deep purple though (I've done what I think is deep purple using Chefmaster colors straight out of the container), so you needn't go to powders and the added step of pre-dissolving them, IMO.