The depth of field in macro pictures is inharently shallow and you have delt with that fact well. I get the feeling that this picture was taken on a dull overcast day which is the reason it has a grey cast to the color.
Interesting composition, and I like the simpleness of the colors. It is a good picture, but I think it would be more effective for this challenge if we could see the texture of the grass more, or if there was more of the ball in detail. The roughness of the grass and the smoothness of the ball would be nice contrasts. karmat