How do I add custom color forces, trails, grips and so to my set to make it look more awesome, when I do the sale thingy?

As well as how do I change the background?

P.s. I don't have the force items and so, but I'm only doing it to sell my sets.
(e.g. if I make 40k Azurite set, I need Az force visuals, but I can't buy it just for the set.)