'wear white. mind losing.'

Call questionable balls his way, not yours:
You lose the point but have your concentration,
The grail of self-respect. Wear white. Mind losing.
Robert Pinsky, "Tennis." Sadness and Happiness. Princeton University Press, 1975. Longer excerpt available here.

Photo: Gobert showing a tennis racket by Agence Rol, 1913. National Library of France, Public Domain. Discovered here.