> 1- Pick the color of a white structure (I choose a ceiling near a
> fluorescent light); 2 - Aplly an overlay layer with the inverse of this
Try changing the blend mode of the "overlay layer" to color and adjusting
the opacity to taste (maybe 50%).
> This makes a filter that I can apply to the other slides (as a starting
> point) much better than all my other tries. While it cannot correct for
> uneven illumination, results are very agreable and also very plausible.