How to change background color in an image with a single layer?

[The Instigator]

I need to change the background color of a PNG image that has only one layer, using PhotoShop 2018. You can't select everything else and mask it because it's a very complex image, and the Spot Healing Brush tool doesn't seem help much because the color I'm trying to change is very subtle and only appears in certain areas.

There must be an easy way to just change the entire background color, but I have yet to find it.

Can anyone help?

[Stephen Marsh]

Another option is the Filter > Camera Raw Filter.

Here I have set the white balance to the buff background using the eyedropper (Basic) and have also applied Vignette reduction (Optics).

Again, just a start point, more subtle and finessed results are of course possible.

[The Instigator]

Hmm… I don't see a Camera Raw filter in the Filter menu for Photoshop CC 2018.