I was totally ignorant about there being different sides of float/greenhouse glass until a couple of years ago.
Greenhouse glass doesn't have a tin side, it's rolled flat, rather than floated on a bed of tin, as it doesn't need to be as smooth (optically clear).
The different shades of green are probably just down to different batches being slightly different formulations. I've had some pieces of float that had no obvious green tinge at all, although you can get low iron float glass for optical clarity (often used in things like display cabinets so they don't alter colours of products, etc)