I used to own a deep forest green Mustang and most of the time it was too dark, but when the sun hits it right it's a beautiful color.
I don't like black ones because a lot of people think it's automatically cool because it's black. Having a black car doesn't automatically make you bad-a$$. But I admit, a nice black one looks good.
I also dislike grey cars, because at least where I live there are too many grey cars around, mostly company cars. Pick grey if you don't want anybody to notice you. Pick grey if you don't want to pick a real color. I don't have a thing against a grey mustang in itself, I just don't like making your mustang into something that won't stand out among the (grey) crowd. I like bright colors on a Mustang.