The homeworld of the Rainbow Warriors is a planet called Prism. Almost nothing is known about it in official Imperial records. It should be noted that in the official records of Space Marine Chapter Homeworlds, there is a map displaying the galactic locations of the various Astartes Homeworlds. But in the case of the Rainbow Warriors Chapter, instead of displaying their planet with the Chapter's name, it simply says "record deleted" where their homeworld should be. By looking closely, it is clear that the Chapter badge of this deleted Chapter is that of the Rainbow Warriors.