I have somehow and accidentally changed the "background color" of my photos - I don't mean the workspace around the photos, it's the canvas INSIDE the photo frame. It used to be transparent, but now there is a yellowish/beige tint inside the photo frame. I see this yellow color in the grid when I create a "New" photo and when I open existing photos. It looks for all the world like a yellow/beige filter. It doesn't actually change the photos themselves - when I use them in other programs the colors are normal - it's just their appearance in Photoshop that's wrong.
How do I change this back to default (transparent)?
I have an ancient version of Photoshop - version 5.5.