I've seen two union electricians go into a drunken rage arguing either way.
I've seen them both ways all over the place although I've never been to Colorado so maybe thay are all the same there:)
I don't think there is a code on it here as when our office was rewired they put the ground up and we asked them to change some of them. We have alot of large power-pack plugs and they don't work well with the ground up. Inspector approved them both ways.