Are you thinking of creating a website based on one color? One cool tool you can use is a Color Palette. This particular tool will create for you 10 shades of the base color with varying degrees of opacity. The top row emulates opacity over a white background, while the bottom emulates opacity over black background.
The opacity values are 100% opaque, 75%, 50%, 25% and 10% on the top row. The bottom row begins at 85% rather than 100% and continues on as the first. To make it more interesting, you can use different colors other than a white and black backgrounds. I use the color #365215 for this blog. Here is the varying shades of colors using this tool.