I've done some design work in the past for the staffers and stuff, and I could be wrong, but I do not think there is a layered version of the logo. Just flattened already. When I needed to make it a different color, which I did quite a bit as I made the businsess cards for everyone, I made it greyscale, played with the levels a bit to get a nice contrast, then put a solid color over it on another layer and change that layer to color or multiply depending on the color itself.
I'll probably end up doing that then, if no .PSD exists. If the original .PSD was lost, then that was an epic fail though.
Either I'll do something very similar or I'll re-design the entire damn logo. Well now ... now that I think about that ... that might not be a bad idea. Hm.