A program to develop calibration services for color-measuring instruments has been established recently at the National Institute of Standards and Technology (NIST) to address commercial and industrial needs for higher-accuracy measurements of displays. In particular, a reference spectroradiometer has been built with the goal of enabling measurements of displays with the smallest possible uncertainty. The instrument has been characterized for wavelength error, variable bandpass, stray light, linearity and random noise. The accuracy of color measurements with this instrument has been assessed using detailed simulations incorporating the measured performance characteristics of the instrument. In the simulations, the uncertainty in color measurements of sixteen CRT and LCD display colors was calculated. The results of the simulations imply that the instrument is capable of measuring colors of displays with a combined standard uncertainty of approximately 0.001 in chromaticity (x,y) and 1 % in luminance (y).