This is a MATLAB implementation of the Color Frequency concept introduced by T. Kashiwagi & S. Oe.
With this script, you pick a color image and then it computes the color frequency image. The color frequency image is an image where the pixel intensity represents the frequency of pixels in the original image that have that same pixel color as that pixel location. For example, in the screen shot, the blue sky looks bright because there are a lot of similarly colored blue pixels in the image. Everywhere there is a blue pixel in the original image, it will have a high value in the frequency image because the frequency of blue pixels is high.
(If you replace imshow() with image(), and comment out the imwrite() function then you won't need the Image Processing Toolbox.)