I use green/green and here's why. I used to buy yellow/green thinking the contrast would help, but really it doesn't. There really is no confusion as to which is front or rear, or in the case of a three dot setup, which is the middle simply because if you're holding the pistol like you normally do, you'll never have an issue. In other words, you have to be holding it obviously wrong in order to have the sights not properly lined up, and you'll know it too, it isn't easy to hold it that wrong. Yellow or orange fade a LOT faster than green as well so the service life will be shorter.
"There is a principle which is a bar against all information, which is a proof against all argument, and which cannot fail to keep a man in everlasting ignorance – that principle is condemnation before investigation."