I've been scanning old color negatives, mostly from the 1970s and 1980s. Many are coming up real good. However, there are quite a few that show problems with the colors. Typically, the issue is that the scan will show bluish highlights. These pics look really awful. By bluish, I mean cyan. The colors can't be corrected simply by adding red, because that affects all the other tones too.
I've had some success in improving the colors by using Split Toning in Lightroom. This allows me to add red to the highlights, balanced with cyan as necessary in the medium and darker tones. However, it can take a lot of trial and error to get something that looks reasonable. And it seems every photo is different, meaning I have to experiment anew with each.
There are only a few scraps of info on the Web on color shifts in old photographic materials. Several sources suggest that the cyan dye tends to be the least stable. But I haven't found anything very useful on the systematic restoration the colors of scanned negatives.
Some of this no doubt applies to slides too. Slides also show color shifts. But the dyes in slides will vary by the slide chemistry (Kodachrome vs Ektachrome), and may differ from negative dyes too.
I suppose the ultimate way to fix colors would involve adjustment of the individual color curves in Photoshop. I don't use PS, but might have to start. Anyway, I think it might be hard to figure out how to do good and consistent corrections from scratch. It would be nice to know about the principles, and some general rules.
So I'm asking if anyone has experience in this, or knows of links to resources.