The physical additivity of optical-see-through (OST) augmented reality (AR), where display and the real-world overlay with each other, impacts its color appearance. We explored this unique dynamic by looking at the effect of background correlated color temperature (CCT) on AR color appearance with a color matching experiment between a prototype OST-AR RGB system and daylight spectrum reproduction. Different background CCT, luminance levels, and two stimulus types [simulated two-dimensional (2D) disk and three-dimensional (3D) cube] were examined. We found that when the background color is inconsistent with the stimulus providing conflicted cues, matched colors in AR shifted towards the background. The luminance matched on the 3D cube is higher than the 2D disk, suggesting the impact of context on the AR appearance. A controlled metameric matching group between daylight reproduction and LCD or CRT did not show the shift, indicating that the appearance shift is not due to the RGB-spectrum metameric matching, but due to RGB foreground-spectral background interaction beyond simple additivity. How perceptual weighting on the foreground and background is modified to predict the appearance as a function of additivity is discussed.