Before you were given the drops did your vet test the eye? The greenish color you see could still be the results of the dye used during the test. Which causes a fluorescent effect making any marks, knicks, ulcers etc easily visible under light. Of course if it's been quite a number of days this is unlikely.
I had no problem with my mare when she was on them for an eye ulcer except her sensitivity to light lasted longer once she was done with them. The vet told me it was more than likely because of her blue eyes.
My best guess is that the cloudiness is a result of the meds, probably working! However, my advice to you is don't assume that's what it is. I would at least make a call to the vet and see if this is a common occurrence (whatever the horse is being treated for) while on these drops. You don't want to mess around with eye problems. So make the call!