I assume you're talking about the amal valve?

If so I've been told by my tuner that the the black ones are used on cossies and the brown ones are RS Turbo ones.

My amal valve packed up on my saph when it was being tuned, but i brought with me a brown one. When I gave it to the guy doing my car, he said it was no good as it wouldnt be able to handle the increased boost pressure like a cossie one.

How true it is, i have no idea.