Why is the side of my glass?

Question

When you look at it really close its green

Answer 1

also, there could be something green behind the glass

Answer 2

Modern everyday glass (the type used for windows and mass produced drinking glasses etc.) has a slight green tint to it due to iron oxide impurities. This tint is too faint to be noticed in thin sections such as windows or clear bottles but is noticable in thicker sections. When you look at the edge of your glass (or more noticeably when you look at the edge of a sheet of glass) you look through a thick enough section to see this green tint.

Answer 3

I can think of a couple general possibilities that would make you see a rainbow of colors (and maybe just green if you look a certain way).  One is that it's some kind of dispersion effect--like a prism.  Another is some kind of interference effect (like an oil slick).  But you'd see other colors if you looked at different angles.  So probably either the water is greenish or the ambient light is greenish or the glass itself is a little green.