Philly: That is correct. Choose the level of transparancy desite and then 'apply'.
This is true for Vista. In XP, can't say as My system is Vista. Also, you might want to create a substyle for the skin you wish to change as doing it as above will change the transparancy for all skins. I never tried to create a substyle for MyColors skins, but it should work.
I.D. did a set of Tutorials "Walk Throughs" on WB6. You can access them through his Personal Pages under Articles. He also did a Vid on recoloring in WB6.