I was thinking of a keyword that changed based on the card's color.
Apotheosis (cost) - (You may cast this for its Apotheosis cost. If you do it becomes X with Y (based on its color) in addition to its other types.)
If white: become an Angel with …
A Dominaria twist on Landwalking:
This was a twist on the keyword Crew, but I'm not sure if the wording is entirely correct. Thematically, it should really be a land, but it doesn't work under land rules.