Removing color casts
Old photos can fade or get some horrible changes in color. This photo from the seventies has just such a cast. (As well as some textured paper that a PITA.)
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There are multiple ways to get rid of a cast. One of them is with a simple white balance, as done here in Snapseed. It does a good job here, because the one young lady has a white shirt, and I can use the shadow to set a WB point.
If her shirt was cream or pink, however, there might have been no WB point. You can then use a technique I adapted from Photoshop, using MaxCurve.
You need to adjust the Red, Blue, and Green curves using a histogram. You will see that the Red histogram does not go all the way to the ends. I pull the ends of the curve in to the ends of the histogram, and now the histogram fills in from end to end.
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Doing that with all three curves (and the blue one needed a major change) gives these results.
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