Reader Darragh Egan sent me images of Maria Sharapova's and Serena Williams' probable future dresses.
For the French Open Nike dedicated this olive and black Maria Statement Set Dress to Sharapova. As for Serena, the Statement Rally Dress she is expected to wear is all green, in three shades of the color.
Wimbledon dresses are, of course, traditionally white, with touches of yellow for Maria Slam Statement Dress, and touches of pink for Serena's Statement Baseline Dress.
The French Open dresses are not impressive to me, at least in the photos, but I believe that Serena's dress will look great on her and on clay. Wimbledon dresses I find cute, especially the back of Serena's dress.
Additional info: Here you can see the orange dress Victoria Azarenka is expected to wear at the 2012 French Open.