Blue is the colour.
At least it will be in Madrid from this weekend for organisers of the Mutua Madrid Open have taken the decision to play the tournament on blue, rather than the traditional red, clay.
As you can see from the picture above, it's an unusual sight to see a court in such a colour at this time of the season.
The thinking behind the idea - the brainchild of long-time tennis promoter Ion Tiriac - is simple.
The yellow ball is easier to spot on a blue background, both for players and spectators, at the venue or via the TV.
That reason has been behind the move to blue hardcourts at both the Australian Open and the US Open in recent years.
Tournament director Manolo Santana insists: "All we are doing is making it easier for fans at the venue and those watching in television to follow the game.
"In a world where the competition in gaining audiences is ferocious, tennis must also evolve."
Explaining his thinking, Tiriac added: "The Mutua Madrid Open is a tournament that is continuing to work on its own personality and that wants to reinforce its identity.
"Blue will now be its distinctive colour, its trademark, but because of that it doesn't mean it will cease to be one of the top claycourt competitions like Roland Garros, Monte Carlo or Rome."
However, the acid test for the decision has yet to come. Players will be asked about it as soon as they arrive in the Spanish captial with questions coming thick and fast seeking their opinions about how the surface plays. If it differs from the red clay they are used to - and early suggestions are that the ball is bouncing lower - you can bet your bottom dollar complaints will come.
Andy Murray is happy to give the new colour a chance but underlying concerns came in his comment that he has "no idea how the surface will play".
Meanwhile, local hero Rafael Nadal has already gone further, describing the move to blue as a "mistake", while women's star Sam Stosur recently told thetennisspace.com: "I can't say I'm that excited or pleased about playing on the blue clay in Madrid. I don't think it's a good idea changing the colour of the dirt."
Given the process for producing the blue clay does differ from making the better known red dirt - it is not simply a case of dying the red clay blue - there would appear a decent chance that at least some players will not be happy with conditions.
For the blue clay production, white clay is first needed - that is obtained by extracting the iron oxide from the natural clay which is mixed with water to form a block.
The white clay obtained is treated by a blue dye before being heated to a temperature between 900 and 950 degrees Celsius - lower than the heat for the production of red clay.
The bricks produced are then immersed in more dye for 24 hours before going through a drying process.
Finally the clay is ground down and sifted to produce the precise grain size - between 1 and 1.5mm. In total, 3.5 tonnes of the stuff is required per court.
Here endth the science lesson.
It will be interesting to see how things unfold in Madrid, particularly given it is such a major tournament - one of the Masters 1000 events on the ATP World Tour and a Premier Mandatory week for the WTA. Players are also desperate to find good form on the surface ahead of the French Open which is just four weeks away.
Whatever the future holds for the blue stuff, the decision to use it has already had an effect on other tournaments.
Organisers at Roland Garros have already announced they will have a pink claycourt during the French Open, although significantly it will not be used for main tournament matches.
It is instead being used as more of a publicity stunt - promoting the tournament's ladies' day which comes on June 7 when the women's singles semi-finals are due to take place. Court One will be turned pink and will play host to two women's legends matches.
Critics say Madrid's move to blue is also nothing but a PR gimmick, although if that is the case it has certainly worked.
We await to see what unfolds with bated breath.