Green khakis go with just about anything, but you would do well to stay away from wearing more green on top. A nice black or beige button-down would be your best best. Depending on your skin coloring and the particular shade, you might be able to get away with yellow, blue, or grey.
Well to be honest, green khakis is pushing it as it is. I'm not sure how the general public would feel about a color of the rainbow as pants. Unless you're a young teenager going through "that stage. " But, if your green khakis are a must, I would stick to white, black, or brown? No red or purple.