Spray Mount or Photo Fixative spray on colored paper?

I did some silhouette cutouts of my nephews/niece on acid-free colored Caslon paper. Now I want to mount them to white caslon paper which I will frame. I’d like these to last “forever” and therefore not discolor (more than they will from fading over time)

What’s best, good ol’ spray mount, or should I use photo fixative spray?