Apple 2 watch has a solid light blue/green screen? What do I do?

Did you try a hard reset? Press the Digital Crown and the side Button until it restarts and you see the Apple logo. If you're lucky, maybe it's only a software bug.

Try unpairing and re-pairing. If that does not work, you will have to contact Apple Support to repare it or have a replacement.

That's almost certainly a hardware issue. Contact Apple Support and arrange to have the device inspected and serviced.