I use a number of different things on the helmet shields. I think we all know nothing is really going to stand up to the intense heat we face, but what I have found to work is.... Regular leather dyes if you can find the color you want, these work the best. When you cant find the color you are looking for, I use acrylic paint with a tad bit of water mixed in.
If I am going to do any larger area's of color with paint, I use Angelus paint to avoid cracking. Also, I really recommend Springfield Leather. They are very helpful and have quick shipping.
If you guys have any questions feel free to inbox me.