You can also run the ribbon through an ink pad, but I make too big a mess when I do it that way! I still get inky with this method, but it's not quite as messy for me.
Another way to color ribbon is to dampen it and then put it on a bowl with a few drops of reinker. You'll need something to stir the ribbon around to saturate it with color without totally inking your fingers.
If you color your own ribbon, please post a link in the comments field so we can all check it out. Thanks!