The present application includes methods, systems and computer readable storage devices for determining a color score for at least a portion of a biological tissue. The subject matter of the application is embodied in a method that includes obtaining a digital image of the biological tissue, and receiving a selection of a portion of the image as an evaluation area. The method also includes determining for each of a plurality of pixels within the evaluation area, a plurality of color components that are based on a Cartesian color space, and determining, from the color components, a hue value in a polar coordinate based color space. The method further includes determining a color value based on the hue value for each of the plurality of pixels, and assigning a color score to the evaluation area based on an average of the color values of the plurality of pixels.