I found a nice Vim color theme called Wombat.
To install the Wombat scheme, download the file from the site above and put it in ~/.vim/colors/. You can then enable it in your ~/.vimrc file with the following line:
(Replace the word wombat with the name of your desired Vim color scheme. I'm on Ubuntu Dapper with Vim 7, so the locations of your files may differ.)
My favorite Vim scheme is the Desert scheme, but I don't like the green color when in visual mode. So I created a custom scheme by copying the file /usr/share/vim/vim70/colors/desert.vim to the desktop and making a couple of modifications:
I changed line 22 from let g:colors_name="desert" to the name of a new Vim color theme. Then I changed line 49 where it says hi Visual gui=none guifg=khaki guibg=olivedrab. I changed khaki to #000000 (black) and olivedrab to #c4c4c4 (light gray). Then I saved the file with a new name that matched the name that I gave the scheme inside the file.
Here is the original green highlighting the in Desert scheme's visual mode:
Here is the desert scheme with my modified highlighted color:
This is the Wombat color scheme for Vim — it's a nice theme, but the highlighting is a little faint. It could be changed by using the instructions above:
Type :hi to get a list of entities that you can change the color on. It's fairly easy to make a custom syntax highlighting file in Vim.
This is what the Desert color scheme looks like in Vim 7 on Ubuntu 6.06: