The uncertainty associated with the quantitative description of the color of an object is often necessary for determining the acceptability of that object for its intended application. Uncertainties are also required for establishing the traceability of a measurement to a national metrology institute. A systematic, analytical approach to uncertainty analysis, which conforms to currently accepted practice, is presented for reflectance colorimetry. Two important concepts are stressed the measurement equation describing the relation between signals and spectral reflectance factor, and correlations both between signals at the same wavelength and between reflectance factors at different wavelengths. The approach is illustrated by considering representative object colors and instrument parameters.