1. A method for adjusting color balance for an image, comprising: capturing a plurality of calibration images of a calibration target, wherein the calibration target includes a color reference region illuminated by a light source having a distribution of frequencies that cycles over a fixed time period, wherein the calibration images are captured over a calibration period that is greater than or equal to the fixed time period, wherein each of the plurality of calibration images is associated to a time identifier, wherein the capturing includes capturing for a determined exposure time a subject image of a subject illuminated by the light source; associating exposure time data to the subject image; and calculating a color balance adjustment for the plurality of calibration images, for forming a time-dependent color spectrum model of the color balance adjustments, wherein the color spectrum model models changes in the light source over the fixed time period, and wherein the calculating includes calculating at least one subject color balance adjustment for the subject image from the exposure time data and the color spectrum model.