I think he or she was trying to mute the colors slightly. A rainbow hairstyle probably would've been overdone on a human RD, while in the series, the sky blue goes ell with the mane because rainbows are naturally viewed against the sky. But I like your hair color choices, too.
These are mind-blowingly fantastic. I loved to identify the outfit and origin of each individual pic, as well as the theme of the row. All those hours you spent on this definitely show. I can't even find a favorite, they are all so good!