Yes, Rosettes would benefict a lot with the use of color. Maybe that's the only thing not-so-clear in the game. I'm really impressed with game link mode, so well made and designed, with mirror movements, info text... congrats!
I actually had some time to test this out over the long weekend and have created a "Deluxe" version which has colorized tiles and sprites when running on the Game Boy Color.
Give royal-ur-dx.gb a try on the GBC or emulator in GBC mode to test the colorized version, let me know if there is something that could further be improved!