"I don’t think I ever paint the color accurately. It’s a funky color. There is a whole debate over the color of tennis balls. Are they yellow or are they green? I think that every tennis ball shifts between that range in the course of their life. They start off neon, like a toxic sludge, but once a ball starts to lose its fuzz and pick up the residue of whatever surface you’re playing on, they get dull. I would say they start off neon green and go more toward yellow over time."
Said Eddie Martinez, quoted in "7 Questions/75 Artists/1 Very Bad Year" (NYT).
Lots of pictures at the link but none of Martinez's tennis balls! I went looking and found this video of him painting: