Lancelot (Blue) is the first monster the player gets. It is used to teach you how to use, raise, evolve and sacrifice one monster to evolve another monster. R rank is lowest rank (R -> SR -> SSR -> UR). Only an SR (or above) rank monster can evolve up to 10 stars and have a different appearance. R rank monsters can't evolve beyond 5 stars.
Flash (Orange) is the monster the player could gets from normal summoning. It's 4 star SR rank monster that can't evolve beyond 5 stars. It also don't change appeared when evolve. It's a monster that was mean to be a scarified monster to power up higher rank monster.