A few of the clothing items for example look like they could be made of silk, and having whatever piece of clothing or armour they’re layered on top of show through slightly would add the to visual appeal of the characters, particularly if your overlaying say a really bright sash on top of a darker piece.
I’m already doing it outside the program anyway by exporting numerous images with various things on them, then photochopping them together as required. Like Kelemelan said, it’s just unwieldy, particularly for for someone like me with little to zero know-how in graphics programs.
GIMP, while I use it, I find a particular PITA to accomplish things in.