Djokovic, who starts defending his title Tuesday, believes the governing body of men's tennis didn't adequately consult with the top players before allowing the change.
"The only thing that is a little bit disappointing from a player's standpoint is that this is decided without players agreeing on it," Djokovic said Monday. "If you don't have, especially, top players testing the court and agreeing for this change, that should mean something. They should have value in what they say.
"Unfortunately, that wasn't the case. The ATP should have done a better job in representing the players' rights."
On Friday, Nadal said the ATP made a mistake by allowing the surface change at a Masters Series event.
The ATP said it approved the move after all necessary tests were performed on the Madrid court, and that the surface's future will be evaluated after it receives feedback from players this week. The ATP calls the change "innovative" and says the color makes it easier for players, fans and TV viewers to follow the ball.
After a few days of play, the main criticism has been that the surface is too slippery.
"I hope that we don't have injuries and that we can have a decent week of tennis here," Djokovic said. "It's definitely interesting for everybody to see what will happen throughout this week. It is different. I tried to prepare for it as best as I can."
"I don't think there is a big difference between the blue and the red," Williams said. "I think it's the same except for it's a different color and you don't get as dirty, which I love."