I'm sure that we can find it if you provide some additional information. It may not be on this site if it's a loli game. You say that the heroine's hair color changes to pink/blue as she transforms? Is the game divided into two parts, one being every-day life as her going to school and stuff and the other part her transforming and fighting the forces of evil?
Is the game set in a fantasy world, a contemporary setting, or sci-fi?
Aside from defeat rape, does it feature any particular fetishes? Like, are tentacles or monsters the main antagonists or is it humans?
Do you remember what eye color the girl had or the color and style of her magical girl costume?
Does the girl have a mascot who gives her magical powers, like Kyubey from Madoka or Luna from Sailor Moon?
Any other details, no matter how insignificant, that you may be able to recall?
Some additional guesses:
https://f95zone.to/threads/magical-girl-seraphier-v1-03-magical-ponpon.195862/
https://f95zone.to/threads/maken-shi-sara-final-kushimoto-house.103739/
https://f95zone.to/threads/magical-girl-lunas-misfortunes-1-09-namaste-koboo.115811/
https://f95zone.to/threads/magical-girl-magical-heart.135907/
https://f95zone.to/threads/translation-request-hitsuji-girl.117881/