The appropriate and skilled use of color can draw people into your content. 

The links are for those of us who never studied art or paid attention in art class in grade school.

Sites to help learn Color Theory

• About.com - Basic stuff here.  Basic is good.
  
• Color Matters - Just found this site.  Looks pretty awesome.
  

Sites about using color:

• COLOURlovers - An excellent resource for finding creative color palettes and the latest trends in color use in web design.
  
• Color Blindness - Topics in Usability - About 15% of the world has some form of colorblindness.  Here is how to design for them.
  
• The Meaning of Colour in Web Design - Colors evoke emotional responses.  Though subjective to be sure, this site can provide some concrete guidance in creating the right feel for you site.

 Palette Generators:

• [ws] Color Scheme Generator 2 - I use this all the time.  Creates a plethora of color schemes off of a single color you provide.
• Color Palette Generator - Feed it a picture and it regurgitates a color palette based on the picture.  How cool is that?

Essential Firefox Plugins:

• ColorZilla - Extremely useful for pulling the Hex or RGB color codes off any pixel on a webpage.
• FireColor - Color Picker, Plus extensive code conversion.
• Palette Grabber - Creates a color palette for Photoshop, Paint Shop Pro, GIMP, Flash, Fireworks, or OS X based on the current page.