First off I have never worn a chastity cage or belt for more than 24 hours, but I have forced myself to quit masturbating for over 5 months, without any cage or belt, which has been very difficult.
I have had a problem called vasco-congestion, commonly called blue balls, wherein my testicles get swollen and painful. Mine do not literally turn blue but this can happen to some people.
Have you experienced a similar issue?
If so... applying ice or other cold compress to the testicles helps relieve the pain.
If not... oops, this is irrelevant for you.