I apologize if this has been suggested already, searching for the keywords trade and gem bring up many results.

To craft gemstone dragons, it generally takes two large gemstones of a certain color. However, just trading two super rares gives one two large gems, and there are many leftover small or even large gemstones. Most people don't want to craft multiple ruby/emerald etc. dragons, and would prefer to craft gemstone dragons that they do not have. These additional gemstones in the inventory are just a waste, and I would love to see something implemented where we could trade small and large gemstones of colors we don't need for colors that we do. I'm sure TL could think of a suitable ratio, or additional materials needed to transform the gemstones.