Actually, as is often the case with
vim, if you can think of the feature, someone has probably implemented it.
In this case, you are probably looking for the Colorizer plugin. Note that though this plugin “works best” with
gvim, it supports 88 and 256 color terminals.
From the script site:
The idea is to highlight color names and codes in the same color that they represent.
The plugin understands the W3-Colors (used for CSS files for example), the Color names from the X11 Window System and also codes in hex notation, like
#FF0000 (which represents Red in the RGB color system). Additionally, it supports the CSS color specifications, e.g.
rgb(RR,GG,BB) color representation in either absolutely values or as percentage and also the HVL Color representation like
Edit: You did not mention what operating system you're using, but the installation is fairly straight-forward even if done manually. However, if you are using Arch Linux, I packaged this plugin and it is available for installation through the AUR.