2 days prior to a regatta, the race committee posts the sailing instructions.  The SI's show mark #2 (the further upwind weather mark) is yellow, and mark #1 (the weather mark closer to the starting line) is red.

At some time between the original SI posting and the evening before the race, the RC posts a 2nd version of SI's in which they switch the colors of the windward marks. In this version Mark #2 (the further mark) is red, and Mark #1 is yellow. (see images of the two SI versions below)

The race committee did not post any amendment to the SIs announcing this change, nor do they mention anything at the skipper's meeting.

Which version of the sailing instructions is valid?

Extra details:

Conditions were windy (20 knots), so some competitors on the water (who had looked at the Original SIs) assumed that that mark 2 had dragged from its position to windward of mark 1, to a position to leeward of mark 1.

Thankfully, there were no protests since the leading boats in the race just went around both weather marks, and the rest of the fleet followed them. But had they not, there could have been a protest.