I would imagine that the same amount of light would be falling on both, as they are directly lit by the sun. Giving panchromatic b emulsion as the film, the exposure should stay the same, perhaps up to 1/3 less. That is entirely without taking into account the actual values.
I have found that in similar cases, the sunlit values don't change much. It's when filters and other values within the scene are accounted for, there can be quite a difference.