Would it really be so hard to ask in that thread, or
link to it?
What you want to do is set the Alpha value for a piece of clothing. You have an R, G, B and A slider for some - red, green, blue and alpha. Some of them don't have the alpha slider, but it can still be set by copying the value of one that has it - you do that by clicking the color selection thing for a piece of clothing with an alpha value, setting that to the value you want (0 for transparent) and clicking the icon of an arrow coming out of a square. You can then click the one of an arrow coming into a square on the piece of clothing you want to copy the value to.
Except Maineim explained this all with screenshots already.