upon further thought, it actually doesn’t make sense to not allow new players to draw on something that somebody else drew. The way to determine whether they are doing that would be to store whether they did not draw somewhere and if it is not blank (Institutional white). As that is the case with things people have drawn now, it would also be the case if a second new player were to scribble nearby where the first is trying to draw, and the first would not be allowed to erase it unless they had already drawn there previously. The second player’s scribble would be in the first player’s way, and the game would be telling them to go and find an open space to draw in again. The only solution would be to timestamp every cell, which I definitely don’t want to do.
edit: actually I could just take a snapshot of what cells were already colored when they got there, and let them change any new ones. that would solve the problem.