Don't worry about that, Katie. Generally, the urates will be about 3/4 white and 1/4 "something else". Colors can range from light yellow all the way through various greens and browns.
Just take a mental note of what it looks like. Eventually, you'll get to know the various colors it can take on well enough that if something actually worrisome appears there will be no question as to whether or not it is normal.
It's not a bad idea to bring him into a vet for an initial check up either. I know most people only bring their snakes in when they get sick, but a good policy is to also bring in any new arrivals at some point during their quarantine.
Good luck and welcome to the ball python world...you will soon be addicted...enjoy.
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