You may just be stuck with them, in which case frequent (very frequent) water changes will help control the issues you will have with overcrowding. Frankly, I would consider purchasing a second tank. You can rearrange the fish between the two tanks and get the color you want. You want color? Try getting the neon Tetras in all different colors. But again since you are overstocked already you need to purchase a second tank to handle any more fish. That's why I now have 4 tanks (LOL) I'm addicted. Also since you are having a community fish tank make sure EVERY fish you get has a rating of "peaceful" - skip any that say semi-aggressive unless you have enough of those to fill their own tank together - but keep them away from the peaceful fish. Once I removed my peaceful large Gourami's and put them in a different tank, I left the semi-aggressive Gourami's in their own tank. While they do chase after each other they cause no damage - when I had the peaceful ones mixed with the semi-aggressive ones - it was a nightmare - while no fish died, the peaceful ones were constantly harassed. Now that they are in their own tank they are happier and my semi-aggressive fish have even settled down.
Anyway my point is that there are a LOT of things to consider to solve your situation. Research each species of fish before you purchase them - not just for aggressiveness but for PH, water hardness, temperature tolerance etc.
Bottom line, get a second tank of at least 29 gallons and you'll have the flexibility you want and the space to add colorful fish. Once you've established one tank it's really not that much more hassle to get a second one. (Just don't get 4 like I did, all I do is water changes and filter cleaning LOL - but I also have all the fish I've wanted so it's worth it to me). Since I'm disabled it can be a huge struggle some days but it's also great exercise for me and I feel better than I have in years. But if you are working full-time or a full-time student I would limit the number of tanks to 2 or you're going to feel like you have two jobs and start slacking off on water changes and other maintenance.