It could be he is starting to molt, the colour isn't in the shell but in the flesh and the molted shell will be clear. I also can't see anything else obviously wrong!
The green may just be their colour or something they have eaten, as you stated. There are also some shrimp that can change colour, though I don't think these are those? Going green makes sense in a planted tank.
Unless you are convinced there is something wrong I would just keep an eye oon them. Quarantining and treating with meds will stress them anyyway, which may kill them and so you think they were sick (but they were healthy ones you killed) and everything then gets into a mess, and then you may need meds for stress! Try not to over react as that can be worse for all the parties involved.
Just be very vigilant for now and you can post here as much/often as you want.
Have you checked the water parameters, if they aren't right it could be he is having problems molting?