This is a really cool feature found right inside of Adobe Fireworks. What is great about this feature is that when you blend the colors, they are safe for the web. Many times when I am building site composite, or a piece of web work I would like a mix of two major colors that I am using in the site, or a mix of two colors found within a photo. This is really easy to do inside of Fireworks with the Color Blender found within the Color Palette.
All you have to do is go down to the bottom of the Color Palette. This is where you can control all of the settings for the mix of the two colors. The different blocks are the number of steps in color gradation from your first color choice to the second one. The slider will determine how many steps there are. The default is 15, but you can make it more or less.
To choose your two colors, simply click the square and an eyedropper will come up so you can sample a color from anywhere on the screen. You can do that with the second color as well, giving you an infinite number of color choices.
In the example, I wanted a gradient that was a mix of the purple in the logo and the charcoal in the main header box. I chose the original color for the lighter part of the gradient, and the charcoal/purple mixture for the darker part of the gradient.
Fireworks is definitely a great tool for making mock-ups for your web sites. It is flexible, versatile, and a great web tool.