A. Bitches wear pink. It's a well-known fact.
B. They were all originally color coordinated to their Lions.
By the Japanese version, the Black Lion driver got killed and everyone shifted positions, with the dude in Red taking over, thus earing the Black Lion spot. Allura stepped into the Blue Lion's roll, etc. Eventually, Sven's brother shows up.
By the American version, Sven is away at the hospital for a while. He'll be back later.