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I'll repost a demo and some comments here that I just posted on MrFrenik's sketchbook in case anyone is interested. His aim was to paint a ball under a light source such that "the ball was a rather saturated green and matte surfaced, the light source is supposed to be the sun (almost noon) and the table is supposed to be the ground".
My comments on the demo below: "The basic process is really quite simple: Work out the pattern of light created by each light source (including refllectors) separately, and then superimpose and combine these patterns additively using linear dodge mode. (The shadows will take care of themselves). Apply local colour using a layer in multiply mode.
A couple of points arising from this example: Blue skylight tends to neutralize the yellowish cast of the sunlight around noon, so I wouldn't expect the up planes to be particularly yellowish/orangeish (unless the atmosphere was very smoky). Also, notice that a strong local colour tends to mask the variations in the colour of the lighting."