There have to be about a hundred of these threads but I will give it a go.
Green is bright, you would have to have a very bright background for it to wash out. It is my favorite. I have a TA33G-H on my patrol carbine.
Amber, according to Trijicon is the easiest for the eyes to pick up day and night, but might wash out if used in the wrong enviroment. I have 2 amber trijicon products (accupoints) and like them both.
Red is also very good. I have one red trijicon in my arsenal and like it very much. Some find it harder to see at night. Red probably has the most followers because it is the one used by our armed forces. It is another solid choice.
You really need to get to a place that has all 3 colors and see what works best for you.
Good Luck.
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