While on a trip I took two pictures at the beach. One with Velvia 50 (when the reflections where subdued) and one with Ektar (when the reflections were too harsh to even look at them). The shots were taken reasonably close to each other. The shot taken with Ektar (though challenging even for Ektar) would have been impossible with Velvia. Now with both shots, a simple color match in PS using Velvia as the source and Ektar as the Target, does a SPOT-ON COLOR CONVERSION. (This would not work unless the target and the source are similar pictures). Et Voila.