the only way of finding out for sure would be to have DNA testing done. Blue and green actually come from the same genes, so the fact your eye color is different MAY not mean anything. In most cases of identical twins, there is usually one placenta...twins with 2 placenta are said to be fraternal, however in some cases, identical twins will each have their own placenta! Sometimes, fraternals also appear to share a placenta because they were so close together they they 'fused'. You and your twin probably did not share a placenta, which 'makes' you fraternal, even though there is a chance you may be identical.
I know a woman with 2 sets of twins...her first are SAID to be fraternal, but I can't help but think they definitely are NOT because they look identical. Of course, a mother can spot differences like a freckle/mole here, a slight difference in eye or nose shape, but that alone does not make them non-identical twins! You can be identical and not looke EXACTLY alike! The DNA, of course, is exactly the same, but that doesn't mean you will always look exactly alike!
It is also possible, though, for twins to look VERY similar and not share the same exact DNA.
If you want to know badly enough, fork over the money for DNA testing to find out...otherwise, just live with it! It doesn't 'matter' in the scheme of things really, does it?