Environmental laws mandate the protection of visibility conditions in national parks and wilderness areas from atmospheric haze, which occurs due to the emissions of anthropogenic air pollutants. To calculate the improvement in visibility that results from the reduction of these air pollutants, it is necessary to quantify the relationship of haze to the color appearance of objects being viewed through it. To this end, a field study was conducted in the Great Smoky Mountains National Park in eastern Tennessee. Color appearance of objects was quantified by color matching with a special visual colorimeter. The Hunt94 color-appearance model was used to compare these matches with simultaneous spectral measurements. In addition to the chromaticity coordinates and luminance of the object, the Hunt94 model requires a number of parameters such as the chromaticity of the adapting light and chromatic and brightness surround induction factors, which need to be determined for the outdoor viewing conditions. This article describes how this was accomplished. Although it accounts for differences in viewing conditions between the colorimeter and daylight conditions, the Hunt94 model does not account for the perceptual transparency effect of haze on outdoor color appearance. These results challenge the manner in which current air quality-visibility models are being utilized.