RogueJK
It's not "Rouge"... That's makeup.
I think it only applies to fire, cold, lightning, acid, poison though.
The UA Elemental Spell metamagic applies to acid, cold, fire, lightning, and thunder. With Thunder being the clear winner in most cases due to the dearth of Thunder resistant/immune enemies. (Especially if that element-focused Sorcerer with Elemental Spell also dipped 2 levels in Tempest Cleric to be able to maximize their Thunderball for 48 damage + 6 more per upcast slot.)