If anyone wants to give it a try, I used the Vampire Red (but there are lots of colors I think would probably work well) and put a lot of it in my bottle of conditioner. I wash my hair first thing, when I get in the shower and let the conditioner soak in while I'm shaving and whatnot. Be forewarned, the stuff will also stain your hands but I have found that it washes back off by the time I get out of the shower (I take really long showers, so there is a chance that won't happen for everyone, but if you just wash your hands a couple of times you should be fine). Anyway, just thought I would share my little discovery with you guys.
Keep in mind that the colors olny come out like this ^ if you bleach your hair first. The conditioner method will only give you a slight tint, but mine comes out looking much closer to Vampire Red than to my natural color, Gray-ish Brown.