The ability to predict the long-term outdoor weathering of coatings and printed graphics is essential to many industries. However, this is a difficult task. Rates of photo-oxidation and hydrolysis for different materials often do not increase by the same factors in accelerated weathering tests, primarily because of differences between the spectral power distributions of sunlight and artificial light sources. For some materials, accelerated testing results correspond poorly to phenomena observed in outdoor exposures. Because of these difficulties, few correlation studies have been published. This paper describes a correlation study between a Xenon Arc Weather-Ometer and Milwaukee outdoor weathering. Color changes of signs and printed ink jet media were measured with colorimeters and optical densitometers. Correlations were determined for both individual materials and overall data sets. The merits of measuring color changes with colorimeters and optical densitometers will be discussed. The efficacy of the ASTM G26 and SAE J1960 testing cycles will also be considered.