Oh, rainbow words, my daughter disliked this in 3rd grade (and as her mom I hated it). I am glad to see some kids like it though, it was a real struggle for her to do her spelling homework in the first place, but it became all about the colors and having the different colors, vs. the actual spelling of the word. What saved us was there were alternatives to this, one of them money words, that was even worse! but there were a few easier ones to do
ETA: she had to use one color for one letter, a different color for next letter, I think I like what the above poster has suggested, that sounds more like spelling practice.