The optical performance of an electrochromic window is found to deviate with window color state and with sky condition from clear to cloudy. A new spectral cloud model ALLSKY1 (Soule) is developed and applied to an electrochromic window recently developed at NREL (Zhang and Benson). A comparison in spectral selectivity also is made between the electrochromic window and spectrally selective standard windows. Two series of double- glazed window sections, including the electrochromic window with color state and a series of standard windows with spectral selectivity, were measured for transmittance and reflectance (300 - 2500 nm). A new near-infrared blocking factor, that depends strongly on sky conditions, is developed for warm-climate window applications with cooling load reduction. The color shifts of both the incident daylight spectra from clear to cloudy and the electrochromic window with color state are studied with a chromaticity analysis (CIE 1931 2 degrees). Computed daylight correlated color temperatures show a wide range, with values of 5660 K for clear global irradiation, 6210 K for clouds, and 13,250 K for a zenith blue sky. Chromatic trajectories with color state for transmitted radiation extend further toward the blue to 8180 K for the global and 28,990 K for the zenith sky irradiation.