I will try to link to some examples later but I may have thrown away all of the tinged scans. This userpic was a scan of a graphite (grey) drawing on cheaper white sketch paper - not how it scanned at all.
crossposted to natf
I am scanning from the same sketchbook but different pages, one after the other on the same day and so in the same weather conditions.
I do press it down lightly but if I press too hard the scan is totally distorted.
Some light is bound to get in the sides of the sketchbook.
From one page to the next the color cast will change from grey to pink to none.
The colour cast is always graduated diagonally or from one side/edge of the paper. i.e. it is not constant across the whole page/scan. This means that PS levels won't help much (I have tried that)
Maybe I just need a more expensive scanner...