Biggest is to understand that these fish have a genetic modification so they have special colors. But, there are many of these fish which are fish which are needing to have groups.
The types of fish are Zebra Danios, Black Skirt Tetras, Tiger Barbs (these need groups of fish to hang out with, and Rainbow sharks, which I wouldn't recommend unless you have a larger tank, and plenty of hiding places, they are usually aggressive in smaller tanks or crowded spaces.
The different colors do not matter in the species of fish, Tiger Barbs are often especially needing to have groups.
Males and females can matter. If you can get one male fish to 2 or 3 females for the groups it is better.
This is because males often chase the females relentlessly and having additional females allows there to be some rest time in between individuals females being chased.
Having the appropriately sized tank for the groups of fish you plan to keep. For instance the Barbs Tiger Barbs, are needing a 30G tank, they love to swim, the Danios love to swim too.
Don't get a 10G tank for the fish which need more room, no matter what the sales person tells you. A 20G long tank is a good middle road for the Tetras and Danios, even though the info says 10G these fish really like swimming around and having a group of 6 or more is preferred so they feel safe and have the correct male and female ratio.
Also, regular (not Glo) fish of the species can be really beautiful and cost less per fish.
An example is a Zebra Danio Glo fish is around 7.99 and a variety of Zebra Danio not Glo fish cost around 1.29-1.59 There are long fins variety like longfin Leopard Danio
Just some ideas for beginner fish.
Also read the article about starting and tank keeping in my signature. Knowing about the nitrification cycle is key!