Pictones is a web app that allows you to extract colors from any picture. It works almost instantly and can be useful for a lot of use cases. I think it would be perfect for designing a color scheme around a base image.

Once you drag and drop your image it gives you the CSS, Sass, and/or Less, plus the colors can be output in Hex or RGB.

Pictones Example

What is impressive is how quickly the image is uploaded and the colors are extracted, I am on a fast connection and it feels instant.