What colour are Tennis Balls?

I have just spent a ridiculous amount of time reading about tennis balls today for a very unintersting post I started writing.

One of the things I was reading was about their colour. Not the pink dog balls you can get or kids' balls, but the regular ones they use in tennis matches on TV.

Seriously, its as boring and simple as those two choices!

Thank you for participating :-)

Green

Yellow

Answer the question at dpoll.xyz.