Now come to think of it since u have a 50 gallon and you are going to move your goldfish and plec in it then ur question would be what to put in 10 gallon ... and u said u want something colorful. Hmmmm ..... i would put 2 rams. Just 2 rams and nothign else. I know some people would argue with this but i think if u keep a planted 10 gallon tank with just 2 rams they would do fine. . .
Or just keep livebearers.
Or just keep livebearers.