That's really pretty- just like robin's eggs.Had to be something they fed the rodents- likely "fake food" (w/ food-coloring?) like those multi-color "treats" they sell for hamsters & such? I really doubt they fed them blueberries...
You might expect this from a rainbow boa....[jkg]
Seriously, I've seen pale (dull) greenish ones but not blue like this. TKS for photo. It's probably just from bile salts, but if it persists, or anything health-wise "seems wrong" with this snake, it would be best to ask your vet (to do a fecal exam). Right now I'd say it's likely nothing to worry about- just a "one-off".