There's no rule that says that Red Doors can't start frozen, just that once they've been unfrozen, the Maroon Aura can't re-freeze them.
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Ok. About the
I think the Maroon Doors should be immune to Maroon effect and so on the other dark colors instead.
I was thought a Forest 5-door would become unable to open them in the "classical" way but I found they can be opened if you have at least 1 Green key so it cancels the Forest area with the difference rule. Sorry for this.