Ten Things to Help with Online Color Choices
With the Color Blender HTML color palette generator, you "pick a color value format, input two valid CSS color values in the format you chose, and pick the number of midpoints you'd like to see. The palette will show the colors you input as well as the requested number of midpoint colors, and the values of those colors."
This Color Code Generator/Color Picker gives you colors, RGB, hex, and a test button for each that changes the outer border of the page to your test color so you can see what it looks like as a background.
Learn the basics of HTML color over at Ted M. Montgomery's Color Coding tutorial page.
If you know the name of a color you want to use but not the hex codes or RGB values, give Draac.com's Color Converter a whirl.
Color Design for the Web, a very interesting workshop article by Vaishali Singh, talks about how to get your web site or blog's color design to harmonize with your content.
One of my favorite online generators, DeGraeve.com's Color Palette Generator, will generate the codes and colors to compliment any image you upload (excellent if you're trying to harmonize your web site or blog to your cover art or other theme images.)
See your primary color choice in mono, contrast, triad, tetrad and analogic color schemes on a mini mock template with the Color Scheme and Color Scheme Two generators (warning, addictive.)
Pallasart Web Design's article How to Make Effective Use of Color in Websites takes a look at how people respond to colors and the most effective colors you can use for your site or blog.
GenerateIt.net offers a more simplified but equally addictive online color scheme generator.
If you want to play around with HTML color choices and/or see how your web site or blog template colors will look together, definitely check out Christian Gram Hansen's interesting Unsafe Colormatch generator.