Grave Betrayal doesn't overwrite any previous colors or types. Rather, it adds another color and another creature type.
Grave Betrayal
In a multiplayer game, if more than one player controls a Grave Betrayal and a creature controlled by none of those players dies, each Grave Betrayal will create a delayed triggered ability at the beginning of the next end step. The first such ability to resolve will return the creature. Usually, this will be one controlled by the player furthest from the active player in turn order.
The phrase "with an additional +1/+1 counter on it" means that the creature enters with one more +1/+1 counter than it would normally enter with. It doesn't keep any counters it had on it when it died.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Lucas Graciano
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
