A system, medium, and method converting image colors, more particularly, a system, medium, and method converting image colors by estimating the surface spectral reflectance of a subject in one or more wavelength ranges based on an input color signal and by converting the input color signal into a device-independent color signal based on the estimated surface spectral reflectance. The system may include an image input unit receiving an image, a reflectance estimating unit estimating spectral reflectances of the image in one or more wavelength ranges, a reflectance synthesizing unit synthesizing the estimated spectral reflectances into one spectral reflectance, and a color converting unit converting the color of the image on the basis of the synthesized spectral reflectance.