Understanding chromatic adaptation is a necessary step to solve the color constancy problem for a variety of application purposes. Retinex theory justifies chromatic adaptation, as well as other color illusions, on visual perception principles. Based on the above theory, we have derived an algorithm to solve the color constancy problem and to simulate chromatic adaptation. The evaluation of the results depends on the kind of applications considered. Since our purpose is to contribute to the problem of color rendering on computer system display for photorealistic image synthesis, we have devised a specific test approach. A virtual 'Mondrian' patchwork has been created by applying a rendering algorithm with a photorealistic light model to generate images under different light sources. Trichromatic values of the computer generated patches are the input data for the Retinex algorithm, which computes new color corrected patches. The Euclidean distance in CIELAB space, between the original and Retinex color corrected trichromatic values, has been calculated, showing that the Retinex computational model is very well suited to solve the color constancy problem without any information on the illuminant spectral distribution.