I suggest you to use brown sunglasses lens for tennis. Because brown provides you more contract than other colors. It is better in term of competivision. What is more, brown sunglasses lens can prevent much sunshine into your eyes and stop reflected light from the court. Brown sunglasses are so great that they are called driving lenses and they are really make for sunglasses playing tennis.
The color of sunglasses plays an important role in tennis. When you play tennis, it is a requirement of a different type of contrast-enhancing lens. With a blue or green tint, the blue wavelengths can be passed through the lens, thus highlighting the background and strengthen the comparison with the yellow ball.
Well, as a matter of fact, it depends on your specific needs and personal likes. What I need to tell you is that, your priority is to think about how to better protect your eyes since sometimes your eyes will be exposed to harmful sun lights which will have some bad effect on your eyes. Therefore, polarized sunglasses would be suitable for you. As to the color, I think you should consider dark yellow or just black.