Syntax highlighting allows text of specific file types to be color coded for readability.  Note the additional links and reference to this topic:

• Changing the default syntax highlighting
  

Each file describes a different file type (.txt, .conf, .http, etc.), what words and variables to look for, and how to color them.  You can download additional or custom syntax files for any filetype.  

Syntax files should be located in one of these paths: 

Using a prebuilt highlighting recipe:

You can download text highlighting recipes and add them to your repository to use.  To do this do the following: 

1. Download the syntax highlighting file.  Some good examples would be: 
   
1. Unofficial Cisco Highlighting.  Looks good on a black background
2. Official Cisco Highlighting.  Note that you can find lots of goodies at this site.  
2. Stick the downloads in your syntax directory.  
   
1. In Windoz, it's here: C:\Program Files\Vim\vim72\syntax\
2. In Mac (linux), it's here: /usr/share/vim/vim73/syntax/
3. In unix, it's here: tbd
3. You can see how this highlighting looks on your current file by loading it via the command :set syntax={filename} (without the extension).  For example, if you wanted to test the official cisco highlighting look, you would have downloaded the file ciscoacl.vim into your \syntax directory.  Then while having some file open, like a cisco config file, you would type the following command :set syntax=ciscoacl   
4. If you want this highlighting to be automatically enabled on a specific file type, you need to modify the filetype.vim file, and denote what kind of highlighting recipes you want for each file type.  At it's most basic level this is really easy.  If you want all ".conf" files to be filtered with the ciscoacl formating, you would create the following line: 
   

The challenge is if you want more then one file with that extension.  (for example proftpd.conf* uses an apachestyle formater.)  I have not figured this out just yet.

Making your own recipe:

I was looking for a simple highlighting syntax that would color code comments but nothing else.  With limited google searching, I decided to try this on my own, and realised that it's really easy.  I started with current recipe for log files called txt.vim, made a few changes, and got what I was looking for.

Note: sync, and HiLink are modifications in the txt.vim file.

syn region:

The "syn" region (where every line starts with the syn word) is where we define what matches to look for and what colors to colorcode those matches.  

Within the syntax file are a bunch of ways to match text or strings of text and assign a type of formatting.  Note that the syntax only assigns a "flag" for the area of text.  The color file in use is what defines how that area of text should be colored.  

Region:
A region is defined as having some kind of defined start and end, but within it can be anything. The following statement says to assign the "txtComment" to any string within two brackets "( )" 

The first line in the example below is for anything that starts with a bang "!".  Anything in that "oneline" should be color coded however region "txtBang" is defined.

HiLink:

You can now link the "txtType" to a predefined highlighting format.  

Vim looks to the configuration file filetype.vim to match file extensions to syntax files.  

filetype.vim files can be found in one of the following paths: 

The colors files are lists of predefined color templates that you can choose from for the look-and-feel of your vim terminal.  

a color file can be chosen in the terminal by entering in 

There are a few color files that come standard with all vim deployments, but you can also download others and install them.  One source of color files is http://vimcolorschemetest.googlecode.com/svn/html/index-pl.html

To see the current color file that you are using in your terminal, enter in: 

As an example of a color file, lets look at some sections of the elflord.vim file.  

First we start with the color definitions.  This defines a name of a type of text, and how that text should be modified.  This includes the formatting of the text (bold/underline/etc), the font color, and the color of the background to the font.  It also includes the ability to have this look different depending on the type of a terminal (black/white, color terminal, or color GUI-terminal.)

" highlight name	non-color term	color term	color term font color	color term background	gui screen	gui screen text	gui screen background
hi Normal						guifg=cyan	guibg=black
hi Comment	term=bold		ctermfg=DarkCyan			guifg=#80a0ff
hi Constant	term=underline		ctermfg=Magenta			guifg=Magenta
hi Special	term=bold		ctermfg=DarkMagenta			guifg=Red
hi Identifier	term=underline	cterm=bold	ctermfg=Cyan			guifg=#40ffff
hi Statement	term=bold		ctermfg=Yellow		gui=bold	guifg=#aa4444
hi PreProc	term=underline		ctermfg=LightBlue
hi Type	term=underline		ctermfg=LightGreen
hi Function	term=bold		ctermfg=White			guifg=White
hi Repeat	term=underline		ctermfg=White			guifg=White
hi Operator			ctermfg=Red			guifg=Red
hi Ignore			ctermfg=black			guifg=bg
hi Error	term=reverse		ctermfg=White	ctermbg=Red		guifg=White	guibg=Red
hi Todo	term=standout		ctermfg=Black	ctermbg=Yellow		guifg=Blue	guibg=Yellow