1)Firstly I realised that I had been omitting to click
on 'Reset' at the beginning of the processing of a photo!
You should only start with the settings from a previous correction if the new image has similar problems as the previous one. So starting new by hitting Reset is better in other cases.
(2)I found that with a dificult subject I could achieve a
better result via 'Manual' than in 'Auto'- and I studied
your online User Manual!
Have you tried drawing a sample area on the preview?
(3)I changed to applying the programme to the original tiff
images from the scanned slides instead of lides I had
previously edited without ColorWasher:I don't know if
this would account for a different result.
Yes, you should always apply ColorWasher to the original unaltered image. If you apply color, brightness or contrast corrections with other tools on the image, ColorWasher may not be able to achieve the best results anymore. I will check if that is mentioned in the manual or not.
As mentioned originally, its sometimes difficult to decide which result looks the most 'correct': presumably. if there is some white in the picture one should look at this to see which shows the whitest version: however often there is no white at all: I have to admit to liking photos that have a warm tendency....
You need some experience to decide which corrected version looks best for a certain purpose. There is no such thing as "the best color correction". Whether you correct a photo for neutral, warm or cool colors can depend on the content of the image, your preference, the context in which the image is used and some other things.
ColorWasher lets you remove a color cast and at the same time add a new but different one by changing the Target color. I guess it would be a good idea to add an option to make ColorWasher correct more for warm or cool colors instead of just neutral colors as it does at the moment. Maybe that could be an option in Preference. I'll have to think about it.
Maybe it would also be a good idea to add an option that compensates for the light under which a photo is viewed. For example if a photo is meant to be hung on a wall where a tungsten lamp shines on it, the correction could be made more cooler to compensate for the warm lamp light. But I guess such an option would only be useful for perfectionists.