>>149923642
The important characters are getting multiple cards to represent their different points in the story. Katara's cards are a pure blue for the start of the series, blue/white for book 2 when she's learned healing, and blue/white/green for book 3 when because idk I'm sure their internal logic makes sense for it

We've got a red zuko for book 1, we've seen art for book 2 zuko but don't know the card yet, and book 3 zuko is red/white/black

Blind Bandit toph here is pure green, and Metalbender toph which comes later in the series is green/red/white. Maybe there'll be a two color toph in the middle somewhere. All of this can be seen in the OP link