blue toilet water

I had taken a test recently and i was asked this question. in the bathroom you have a toilet with blue water and the bath tub is discharging blue water out of the faucet. what in the world could cause that. I could have read the question wrong. does anybody know the answer to the problem. it could have been a discharge from the drain.

Cross connection

but it was not one of the answer on the test. i think it had a wax ring, siphon plug and i dont remember the other two possibilities. but it had to do with the toilet.

Water siphoning out of the toilet tank back into the potable water supply through a non aproved fill vanve usually.

I agree with Barry, the only possible explantion is a cross connection.

thank you