The Hue/Saturation/Value filter allows you to replace and correct color or colorize your image based on the HSV color model. The HSV color model is a cylindrical color model. Picture a cylinder. As you move around the outside of all 360° of the cylinder, you move through, Red, Green, Yellow, Blue, Cyan, Magenta, and finally back to Red. Move in and out from the hub of the cylider and you change the saturation (the purity or richness of the colors) of the colors. Move up and down along the cylinder and you change the value (similar to brightness) of the color.
Moving the Hue slider moves all the colors in the image around the HSV spectrum by the specified angle. This can allow for color correction or recolorization of certain parts of the image. Moving the saturation slider will increase or descrease the Saturation of every color in the image, thereby saturating or desaturating every pixel. Moving the Value slider will increase or decrease the brightness of each color in the image. Changes can be narrowed down to only certain color ranges by choosing a range from the Operate On: dropdown list. Available color ranges are: Reds, Yellows, Greens, Cyans, Blues and Magentas.
A more even color can be applied to the image by checking the Colorize Image checkbox. By doing this, Images: In Context!™ will replace all the color in the image with the single Hue you pick, while retaining the Saturation and Value for each pixel. This gives an effect similar to a Duotone or Sepiatone effect.