The next easiest to breed and colorful fish which I like better than guppies is platies and swordtails. They are in the same family and cross readily. This gives you more color patterns and body shapes and types of tail from a small breeding group.

  But I moved on into egg layers. My favorites are killifish. Unlike guppies, platies, and swords though you breed them true to their location codes(where they were collected from the wild). I have 3 types of the same fish. The females can not be told apart except the albinos. The male of the 3 types are easy to tell the difference in. They will cross and produce fertile fry but the offspring bring less money or are unwanted by killifish people. I have some crossed fry of these species right now with the intent of making a better looking aquarium strain than either parent stock. But this type thing is really frowned upon by the AKA(American Killifish Association). If you want to see killifish go to AKA.org and click on The Fish in the right hand colum and then click on killie gallery then click on public gallery. These mostly small fish are as colorful and many salt water fish. Some are useable in community aquariums and others are not. But these fish take more work than live bearers to raise and many require live foods as adults to do great and all fry require some live foods.