This looks less like simple over/underexposure and more like a combination of haze/low contrast and a strong color cast from the aged film/slide or scan.

A practical restoration workflow is:

1. Reduce the haze / increase contrast.
2. Correct white balance or color balance to remove the cast, especially excess magenta and yellow.
3. Fine-tune blacks and whites to restore tonal range.
4. Add a little saturation after the color is neutralized.

In Photoshop or Lightroom, a Dehaze adjustment can help a lot. You can also do similar work manually in other editors, including GIMP, by adjusting levels/curves and color balance.

If you still have the original negative or slide, that’s usually the best starting point. Rescanning the original at higher bit depth can preserve more detail and give you more room to correct color and tone than working from a scan of a print.

So the main issue is best described as color cast plus haze/flat contrast, rather than just exposure.