Even very strong coffee will make a tan color for the rawhide, tried it and I liked the color. To get darker colors, you will need stronger dyes, like aged walnut hulls or oak bark tan. The alcohol and Rit dye will definitely take care of that task of dying the rawhide dark. Post pics, I'm interested in how your experiment turns out. I am planning on rawhide backing a yew bow and thought black rawhide over sapwood would be pretty dramatic.