My female has been known to do that quite often. It's actually how I've ended up with almost all of my pet rats over the years! One time she refused a rat for three weeks before we gave up and got a different one - which she ate!
I doubt snakes can really see color, but try getting a different color rat. That usually worked for Cindy when she was being picky.
Then again, I could just have a wierd snake!
Good luck!
~jennyy
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1.1.1 normal ball pythons (Cindy, Darwin, and Periscope)
1.0 rex rat (Scurvy)
0.1 bunny (Spazz)
2.1 betta fishes (Vicious, Killer, and Butters)
2.2 great danes (Shasta, Odysseus, Merlot, and Watson)
1.0 fat fuzzy mutt (Smokey)
1.1 cats (Thidwick and Turtle)
2.0 horses (Buddy and Sam)
1.0 goat (Billy Jack)
2.25 chickens (Jacques the rooster and his harem)
but what I really want is more ball pythons!