I'm sure the OP is aware of what the "D" key does - hence his question.

The question refers to figuring out how to make the black that goes into the stroke swatch when you press "D" RGB 0,0,0 rather than RGB 35,31,32.

The answer is to change the colour inside the Black swatch. If you look at your Swatches palette, you will see that the fourth swatch in is Black. By default, Illustrator ships with this Black being equivalent to CMYK 0,0,0,100, which makes sense if you're working in CMYK a lot.

If you find yourself doing web work and you wish to change the default Black to RGB 0,0,0 just edit this swatch colour.

To do this on a one-off basis (you have to repeat this for each document), then just double-click the swatch in the Swatches palette and edit the colour. It's not a Global colour swatch by default, so this will NOT change any existing items in your document that have been filled with that colour. However, if you press "D" now on your keyboard, your default stroke will get set to RGB 0,0,0 black.

If you're doing this often, you'll want to set this up as your default colour going forward - every time you open a new document. To do this, you need to edit the default document profile. This process is outlined in Adobe KB article documented here: http://kb2.adobe.com/cps/400/kb400732.html

But for convenience, I'm reposting the information (note these are an AI CS3 instructions, so be sure to check for your version):

To create a custom New Document Profile

To create a custom document profile in Illustrator CS3:

1. Open the New Document Profile file you want to customize in the New Document Profiles folder located in the below directories.
   • Windows: Documents and Settings\(User)\Application Data\Adobe\Adobe Illustrator CS3 Settings.
   • Mac OS: Users\(User)\Library\Application Support\Adobe\Adobe Illustrator CS3
2. Delete any existing swatches, graphic styles, brushes, or symbols you dont want to retain.
3. Do any of the following:
   • Create any colors, patterns, and gradients you want, and save them as swatches. You can also import swatches using the Swatch Libraries command and then move the swatches you want in the Document Profile file into the default Swatches panel.
   • Save any graph designs that you want available in your files using the Graph Design dialog box.
     
   • Create any graphic styles you want and save them to the Graphic Styles panel.
   • Create any brushes you want and save them to the Brushes panel.
   • Create any symbols you want and save them to the Symbols panel.
   • Select the options you want as default settings from the following: View preferences (from the View menu), ruler origins, page origins, print settings (in the Print dialog box, File > Print), and actions.
4. Save the Document Profile file and restart Illustrator.