Can't you set the slot or attachment color? That won't set it for the whole skin, but will do what you need. Another option might be to put the clothes behind the body temporarily. Or you could set the opacity of your attachments in your PSD, do you work, then remove the opacity and recreate the images from the PSD when done.
It sounds like an editor feature, but it's a little hard to fit it into the user interface and make it clear that it's not a runtime feature. At runtime we don't really want to add another way to color attachments, especially since I'm not sure this would be very useful at runtime.
