The Madrid Open is receiving extra attention this year as the Masters Series event for men and women will be the first top-level tournament played on blue clay instead of the traditional red surface.
Roger Federer and Andy Murray are open to giving the unorthodox colour a try, with Maria Sharapova calling it unique and different after practising on it.
Local favourite Nadal, who has yet to set foot on the blue clay, has probably been the strongest critic. He's worried the blue court could "destabilize" his preparations for the French Open.
"I don't support that. The history of the clay court season was on red, it wasn't on blue," the six-time French Open champion, widely considered clay's greatest player, said at the Monte Carlo Open.
"I love all improvements (but this) is a mistake. The players (don't) win nothing. Tennis doesn't win nothing. One person wins. Only the owner of the tournament wins."
The tournament starts this weekend.
Top-ranked Novak Djokovic complains the surface makes it difficult to judge the ball's bounce.
Organizers defended the decision to ditch the red dirt, saying players and TV viewers will be able to follow the ball better. The blue also happens to match the colour of the tournament's main sponsor.
A crew of Roland Garros caretakers is in charge of producing the blue clay.
"The sensation is extraordinary. I was immediately seduced by the quality of this surface," said Gaston Cloup, who leads the veteran crew. "It's not the same colour as traditional clay but it's a traditional clay surface. All products used to make it are identical to usual process, including the dye."
Djokovic and Milos Raonic are among the first players to have practised at the Magic Box centre, with the 23rd-ranked Thornhill, Ont., player tweeting: "Hitting on the Smurf clay, the bounce is lower and the 2 courts I practiced on were a bit more slippery than usual."
Djokovic beat Nadal in a clay-court final for the first time here last year — although it was on the traditional red surface.
"The first impression is that the bounce is a little bit different. Especially with the slice, it bounces low," said the top-ranked Serbian. "It's hard to judge."
Madrid's high altitude already throws a twist into the clay court calendar as the thin air speeds up a normally slow game, so a surface that slows a touch may not be such a bad thing. Spanish player Fernando Verdasco expects the sun's heat to put more bounce into the surface.
"I understand the reasons for doing it," Murray said in Monte Carlo. "It makes the tournament unique and a bit different. Sometimes that's good for the tour. But the timing of it is what makes it difficult for the players. It will be a new experience."
Nadal is used to red — his clothes often end up covered in red clay after rolling on the ground in celebration at nearly every one of his 34 clay court triumphs. Perhaps this season will bring Nadal, who has managed only two victories from four final appearances here, a new look.
"It's a real fashion statement," Williams said on Thursday from Manolo Santana centre court. "I wish I'd thought of it myself."
AP Sports Writer Jerome Pugmire contributed to this report from Paris.