I used a green/brown tonal yarn. Easy to whip up during a movie like... Jurassic World!
Penny was in bed and I put the hat on her:
I feel certain that Penny loves wearing these hats. She purrs the entire time and lets me tie the string into a bow under her chin. And then I take a few pictures and pull the hat off. None of the cats end up wearing these hats for more than 60 seconds.