Article 7.3 of the FIDE Laws reads:
If a game has started with colours reversed then, if less than 10 moves have been made by both players, it shall be discontinued and a new game played with the correct colours. After 10 moves or more, the game shall continue.
I'm not sure what 'colours reversed' means in this rule. It doesn't seem to mean that the colors of the board itself are reversed, because that's fully covered by Article 7.2.2
The two big possibilities I can think of:
The board and pieces were set up correctly, but Black moves first instead of White. [Would this ever actually happen? Everyone suddenly forgetting that White goes first?]
White moves first, but the King and Queen of both players start off in switched positions, so that White has an essentially 'Black' starting setup, and Black has an essentially 'White' starting setup.
If it's possibility #2, then what's the point of Article 7.2.1? It reads:
If during a game it is found that the initial position of the pieces was incorrect, the game shall be cancelled and a new game shall be played.
I imagine that the King and Queen being switched probably accounts for 95% or more of the cases where "the initial position of the pieces was incorrect." Why have 7.2.1 as a rule if it's nearly always overridden by 7.3?
Or maybe there's another interpretation of 7.3 that I've missed entirely. I don't know.