@raolco
I also saved photos I've uploaded on this discussion and uploaded it to an existing listing: No yellowing. Step in the right direction?
Probably. There must have been a transformation in the image format. Is the photo coming off a camera or phone? Is it going through a processor of any sort? Or from cloud storage? Or through some photo manager? Is it camera "raw"? Is it aRGB instead of sRGB? Did it go through a CMYK conversion from RGB? EXIF is not the only data on newer cameras, so perhaps there is more to strip off. And do you have another browser to try, in case a recent browser update is reading something extra from the image?
Look at some of those possibilities. I think eBay's uploader is more primitive than the Forum uploader, so the Forum was more forgiving.
These are a lot of questions intended to get you thinking and looking at settings.