An in-situ color measurement method during heating in an oven is required for optimizing the oven cooking operation. However, conventional colorimetric apparatus is not applicable because such processes usually involve high temperatures and wet surfaces. In this study, we equip an oven chamber with optical fibers connected to a halogen light and spectrometer to perform the in-situ (real time) color measurement. To demonstrate the usability of this method, we observed the color change in white bread heated by hot air and superheated steam at 200℃ as a trial experiment, and compared results from two other types of colorimetric measurements of the samples after heating: a color image recording system using a digital camera, and a commercial spectrophotometer. We found that the value of L* decreased more quickly, and b* had a lower value for baking by superheated steam in comparison with baking by hot air at the same temperature.