Also to add to this, Aki Murase mentions why they made Cure Idol's hair blonde!
"However, once we decided on the colors for the three characters appearing from the beginning—pink, blue, and light purple—we considered and discussed whether it was a problem that there wasn't a single character with a yellow color scheme (including orange).
Ultimately, as an alternative, we decided to compensate for the yellow element by making Cure Idol's hair blonde."
#precure