Betta fishes come in all different kinds of colours!!!! They're beautiful! They are easy to take care of-- you just need a heater and a 2-3 gallon tank.
neon tetras are a fun/cheap way to add color to the tank. oh, and male guppies come in SO many different colors - they are so pretty and their fins get nice and big (for a 2 inch fish). just make sure you don't put any aggressive fish in with them because their fins could get nipped at.
You can get a Betta fish at a pet store for 3 or 4 dollars. They are relatively simple to care for. They require a 2.5+ gallon tank that is filtered and heated to 78-82 degrees. You feed them once in the morning and once in the afternoon (or evening, it doesn't matter once). They only eat a few pellets and the occasional meal of frozen blood worms or brine shrimp. They should be fasted once a week to help prevent constipation.