Why are only some of the characters "color-coded"?
Just for a comment;
The relationship between the letters in their names and the color of their hair is an interesting view point.
Super Sentai's world view seems to be included in this work, and as shown in the picture below, the girls wear Super-Sentai like costumes. I think they were designed to match the color of the costumes with the color of their hair.

Also, it seems that when Japanese anime features young and cute voice actresses, they often incorporate their characteristics into the characters they portray. For example, Kize Mikan seems to be similar to Yamazaki Erii.　This could be a sort of the avatar.