Go to
www.G2USA.com they have some good vinyl dye or so ive heard. Im gonna order mine soon
. Im also heard of SEM vinyl dye. I dont think it really will matter much that your vinyl is black/grey just make sure you get some vinyl prep so the vinyl will "suck up" the dye better and the color will soak in.
Good luck with you interior. Im gonna head over to canadian tire soon and grab the stuff I need to start doing my plastic parts. Which method are you using for them?