Why did my cat throw up a yellowish colored piece of poop?!
this was the weirdest thing I've seen so far
It was not a piece of poop. It was a hairball with some stomach bile on it. ~It can be really creepy seeing your cat do that for the first time, but it is normal. You can however hep to prevent hair balls by grooming your cat (brushing it) regularly.~http://pets.webmd.com/cats/guide/what-to-do-about-hairballs-in-cats
might have been a fur ball with food in it to change the color
Yellowish color sounds like bile? Like an upset stomach
You cat might have eaten its food in a hurry leading to stomach upset. It could also be that it ate more than enough or it is sick. Take to a vet for check up.