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Someone made a plugin to do this: https://github.com/a-sk/sublime-css-colors.  The code is very hackish but you can try it out.  Essentially, it is dynamically creating new colorschemes to highlight to colors.  It would definitely help if one could specify the color of a highlight via the api.
Everyone vote for this.  It will get us one step closer to having a terminal built in to Sublime Text.
>>>Could this get a built-in-feature one day?
No.  Sublime Text's autocompletion queries are generated through python and then processed and displayed through C++ (aside from the default completions which just contain a list of words found in the current file).  So while Jon could make something to do this pre-installed in Sublime, it would ultimately end up being a "plugin" (meaning made with python using Sublime's API).  This could be potentially worse since my plugin is open-source, allowing for new features, bug fixes, and more active maintenance.
EDIT: My plugin called AutoFilename and is now available through Package Control.

This is already possible.  Just open up your user keybindings and add:

{ "keys": ["YOUR_KEY_HERE"], "command": "commit_completion", "context":[{ "key": "auto_complete_visible" },{ "key": "setting.auto_complete_commit_on_tab", "operand": false }]}

If you want to make it filetype specific, you can just add a selector to the context...

How to change console colorscheme: http://www.sublimetext.com/forum/viewtopic.php?f=2&t=4583&p=20807#p20807
I just created a plugin to do this, here: https://gist.github.com/1608287