Color shift upon resave of textures

Working in PS5.5 here, but hoping I can get some insight. I'm pulling my hair out over this one....

I have some lower/upper textures, I have worked with before. They were fine, looked great when uploaded to SL.

Now if open and File>Save As resave them, then re-upload to SL, there's a distinct color mismatch between the upper and lower textures, even though nothing was done but resaving.

I have tried:
- Using the original files on my HD and resaving those
- Downloading my textures from SL and resaving those
- Saving as various file types
- Placing the upper and lower images into the same .PSD file and saving out of that, in case it had to do with a palette in the file itself, which helped a tiny bit

Yes, I'm using a dinosaur version of PS, and yes, it's probably something really silly that I'm missing. Can anyone point me the right direction?

changes since the introduction of Windlight?

*Using the original files on my HD and resaving those* and both files are a good match? did you try adding the files to the same document to make sure they look 'exactly' the same?

are these textures on the body mesh or on prims?

need more info.

could be a problem with colour management - maybe your workflow changes the colour profile of your picture? (like from sRGB to AdobeRGB?)