If a ship makes a move that it can not legally make, or makes no move (forget to give it a dial), then your oppenent picks a legal move for you. In the case of using the wrong dial, if the ship can normally make that move than it is not an illegal move. In the future you need to make sure to read the text on the dial and not take it for granted. I know I make that mistake from time to time only to realize the problem as I go to set up the next dial.
But what if the ship can make the move, but the colour is different?
I don't mind in friendly matches but I'll be running a tournament soon and I just need to pick a definitive ruling for this even if it occurs. I know I've had times where I've put the wrong discs out and haven't realised until the pilot activates. Not that it's something that occurs every round, just once every couple of matches. It wasn't an issue till I got Y-Wings and TIE-Advanced's and I can only see the chance increasing when you add extra ship types into the mix.