I do it this way: list it as one listing (one order), but in the quantity section, list the proper # of items you are selling. Then, in the description area, describe the items accurately. For example, if I was to sell 3 pairs of leggings, I would but 3 in the quantity, and then list:
1 pr raspberry leggings size 2
1 pr lime leggings size 2
1 pr lime leggings size 5
Hope that helps!