D&D General Need help

[Adrik the Barbarian]

I'm writing a lvl 20 campaign and the big twist at the end is supposed to be that the queen they were trying to save for the whole adventure turns out to be an ancient dragon. The problem is I don't know if she should be an ancient blue dragon (she is like a tyrant, trying to take control over the kingdom and the campaign is in a coastal setting) or an ancient green dragon (she doesn't reveal herself until the end and she's very manipulative and works from the shadows)
Edit: I don't think the idea was fully understood so here's some more context:
The dragon is the queen of the land because she killed the heir or previous ruler and is disguised as them. She wants to take complete control over the kingdom but she has a problem: the kingdom's council, practically making it a parliamentary monarchy. To get rid of them, she starts a war between the kingdoms ancient enemies (hobgoblins, kua-toas, etc) and the kindom. She kinda does a Palpatine style move, acting as the ruler of both parts, with order 66 being eliminating her council and gaining full control. The adventurers are caught in all this (they will receive clues that the queen is not who she seems, but they aren't the main focus so it's up to them to arrange the puzzle), thinking they need to fight on the kingdoms side. Hopefully, they manage to ruin her plans, and as a last resort she'll fight the party herself.

 

[CleverNickName]

There's no way to choose, both are awesome. (Just kidding, I voted Blue.)

You could mess with your players and have them encounter an Ancient Teal Dragon. Use the stats for Blue or Green (your choice), and give her both breath weapons (poison or lightning, she chooses which one she wants to use as part of her Action.)

For roleplaying, write her as being both a tyrant who wants to take control of the kingdom and she's manipulative and works from the sidelines, not revealing herself until the end.

 

[Wolfram stout]

I voted green for the manipulation aspect but...if she leads her armies in the field (in disguise) blue dragon if she sends out her armies from her throne room like chess pieces then green.

 

[Deset Gled]

I voted for blue because your description made them seem more obviously evil. The green sounds like there is a very real chance the dragon may convince part of the party that they're actually good. Which could be interesting, but it's a different type of twist from the one you described.

 

[Theory of Games]

I voted that you tell us more about this plot twist you're springing on the players. Are you going to foreshadow it in any reasonable way? Or just "SHAZAM - DRAGON QUEEN!"

 

[billd91]

I'm voting blue because there's a much greater chance they'll have various resistances to poison by the end of the campaign rather than lightning.

 

[aco175]

I voted blue since the campaign takes place in a desert instead of a forest kingdom. Just made this last part up though.

 

[haakon1]

Blue … and foreshadow with electricity, like a static shock if they enter a room she is in.