I'm going to answer the questions to your three (why did you make 3?) threads here.
1. Yes, Tigers do need a heater, like most tropical fish they like the water about 24-26C. So unless you live in a very hot area I would get one.
2. Tigers have a green tint to there black bars naturally, hence the Moss tiger barb. It may have been that they flushed a darker shade when feeding and thats when you saw it.
3. As someone said in your other thread 2 Tiger barbs is not nearly enough, they need a group of 6 or more to be fully happy. I added a group of 4 to my tank about 3 weeks ago and when I put on the lights fish they would go mad and blanch whitish. They have since settled and are now fine. Getting4 more tomorrow!!