The effect on cone excitations of a change in illuminant on a scene may be predicted by von Kries scaling, but these predictions are not perfectly accurate. Here, a non-parametric method was used instead, but which preserved the principle of independence of activity in cone or cone-opponent mechanisms. Performance was evaluated over samples taken from 50 hyperspectral images of vegetated and non-vegetated natural scenes under large changes in daylight illuminant. Taking due account of differences in degrees of freedom, the non-parametric model gave significantly better predictions than von Kries scaling of cone or cone-opponent activity.