Is there any possibility of another color that no one has seen, maybe in different galaxys?

The thing to remember is that we only see a small portion of the entire electromagnetic spectrum. There are all sorts of colors out there that we've never seen because our eyes aren't able to see them. :) Its interesting to note that some animals can see a broader range of frequencies than we can. Bees can see further into the ultraviolet range, so they may see some different colors than we do. Some plants even have patterns on them that are only really noticable in frequencies of light that we humans can't see...so bees may think flowers are even more beautiful and colorful than we think they are. :D