I have a black B17 on my everyday commuter with no problems and a honey B17 on my weekend racing style bike. I also wear 'street' clothes; khakis, etc. and never had a problem.

I rubbed both down with a good amount of Proofhide when they were new and have had no problems with them staining my work pants.

I would avoid wetting them with a towel. I would wear bike shorts or dark casual pants until there was no more dye transfer. However, you may want to talk to your doctor about a bleeding saddle...