The Rainbow Bloon is a bloon that originally appeared in Bloons Tower Defense 2 and has appeared in every other BTD game since. It is the parent of two Black and White Bloons in BTD2 and BTD3 and the parent of two Zebra Bloons in BTD4 and BTD5. Rainbow Bloons are quite fast, having a relative speed of 2.2 compared to a Red Bloon. They are faster than White Bloons but still slower than Ceramic Bloons. In the original Bloons, there is a Helium Bloon, which is also rainbow and is often confused with this.
Rainbow Bloons are relatively strong bloons because, although its own layer is easy to pop, it can spawn a large total of bloons, summing up to 37 bloons per Rainbow Bloon. It is also relatively fast too, having a relative speed of 2.2 compared to a Red Bloon. Many towers or towers with high upgrades are well recommended to dealing with these bloons.
When an Ice Tower upgraded with Snap Freeze freezes a Rainbow Bloon, the Rainbow Bloon will pop leaving behind two Zebra Bloons in its place (shown to the right). Though they are immune to bombs and ice, the Zebra Bloons will be frozen. This one of the few known ways to freeze a Zebra Bloon, the other way is to use the Viral Frost.
If an Ice Tower pops a Rainbow Bloon with Snap Freeze in BTD5 (without Viral Frost or support of a Monkey Intelligence Bureau), the Zebra Bloons just come out unfrozen. The Zebra children will just move at their normal speed.
In BTD2 and BTD3, it is the only bloon to contain two different types of bloon, while in BTD4 and BTD5, it is the Zebra Bloon.
Although the rainbow bloon is a rainbow-colored bloon, it is not the parent of any bloon that is any color of the rainbow.
Before Round 35 in Bloons Tower Defense 4, the game tricks the player by saying there are 3 Rainbow Bloons at the end of the level. There are 3 Rainbow Bloons at the end of the level, but only after 5 are seen earlier in the level.
The official last appearance for Rainbow Bloons is Round 82, where a Camo Rainbow Regen of Doom among with B.F.Bs is incoming, through it wouldn't be a problem because your camo detectors used in Round 78 can usually handle it, it also gives Ice Shards and Bloon Area Denial System ability come through it's spotlight since they can hit the B.F.Bs from behind.