Yes, the three common colours for FKM (Viton) are black, brown and green. When this elastomer became popular the de facto standard in Europe was green and in the US, brown. Our fuel seals for Mikuni BDST are black but as I proved in another video it is the real McCoy. https://litetek.co/MikuniBDSTFuelSealViton.html Took us years to get those damn things perfected. Required a three piece mold. Black FKM is pretty easy to spot because it is more of a dark grey than a glossy black. I'm pretty good at telling them apart by smell too. Since we try to sell everything you need to restore your carbs, I think we have a responsibility to help customers complete the job successfully. A comprehensive guide is really needed because they are tricky little devils.