An image forming system, an image reading apparatus, and an image forming apparatus are provided which can correct color values of images with low cost and high precision and improve the limitations for patch arrangement even in the state of influence of heat discoloration. A paper medium enables temperature correction patches with the same color to be formed at a reference position for detectingreference temperature and a comparison position different from the reference position. The image reading apparatus includes: a scanner that reads respective colors of the temperature correction patches and a colorimeter that performs colorimetry to the temperature correction patches; the image forming apparatus includes: a first calculator that calculates a color difference of color values of thetemperature correction patches at the reference position and at the comparison position; and a second calculator that calculates a temperature distribution; the temperature of the paper medium is distributed in such way that as a temperature difference between a first position and a second position increases, the color difference increases.