If you use text-based Vim, that is, not gVim.
If you use iTerm and its default colorscheme is Dark Backgound.
There is a chance that you may notice a confict between the colorschemes of Vim and iTerm.
There are many blog posts trying to explain to you how the colorscheme command in your vimrc could fail.
But the best bet for you is to use the same colorscheme in Vim and iTerm, like Solarized.
