Visual-domain diffuse reflectance data regularly collected aboard the JR with the Minolta CM-2002 spectrometer can be used successfully to estimate carbonate content by multiple linear regression when validated by a relatively small data set of direct measurements of carbonate content. The major advantage of this indirect estimation of carbonate content is the rapid collection of detailed, high-resolution data. One potential error source in the calibration is the mismatch in depth between the diffuse reflectance and the carbonate measurements from the validation data set. A leg-wide sampling plan that takes into account the locations of the diffuse reflectance measurements would eliminate this problem. Moreover, by coupling the sampling plan of the Minolta measurements to sampling plans for X-ray diffraction, X-ray fluorescence, and other inorganic chemistry and rock magnetism measurements, new data sets for studying the influence of sediment chemistry and mineralogy on color would be readily available, with benefits in interpreting all data sets.