gooHero666
Cosplay clothes are fine. If you want to buy dark cosplay clothes, you can put a white body stocking on your doll first and then put the cosplay clothes over the stocking (you won't see the stocking under the rest of the clothes anyway). Just make sure you wash those dark clothes a couple of times, if the water gets stained when you was it - then you should avoid putting it on the doll. In worst case scenario, it could possibly stain through the body stocking even. I have read this somewhere on the forum. I have not tried any body stockings on my dolls myself, so I can't say for sure what will work and what won't. But as far as I understand, this is one method that might help you.
You can also buy small "test pieces" of TPE from manufacturers or vendors. Put it on a table, lay your clothes over it and put a couple of books or something on the clothes to create some pressure. Leave it for a day or two, if the TPE test piece is stained from the clothes, then you should avoid having it on your doll. Again, this is not something I have tried myself, but I have read about this on the forum.
If you are not sure about certain types of fabrics, you should probably ask on the forum before trying them on your doll. For example, if you find some cosplay clothes made out of leather or something, someone else might have stained their doll that way before you...