You done a great job, it turned out really nice. I wish I would have seen this post a little earlier so I could help you out. For anyone else wanting to do this, here are some tips.
SEM Landau black is perfect for changing the color of the rubber. Just be sure to clean the item well before painting it. The glue method will hold the cap together alright but may come loose if you try to remove the cap from the wheel. We have another method of assembling them that works the best and still allows you to disassemble it in the future if necessary. (Although I don't know why you would.) Drill a 3/16" diameter hole in the center of each fake Allen head being careful not to touch the sides, get 3 machine screws 8-32 X 3/8" long along with nuts, hex heads are best but you can use round ones and grind them flat and shape the sides of the head to be a hex head, paint them flat black and assemble.
Dave