One wrinkle in this is that photons do have indirect self interactions, and any graviton should have self-interaction. [0] But the overall story around colour

One wrinkle in this is that photons do have indirect self interactions, and any graviton should have self-interaction. [0] But the overall story around colour confinement, flux tubes and so constant force required to separate quarks is the right explanation.[1] It is not the self interaction per se that leads to confinement, but that colour seem to be confined. [0] https://physics.stackexchange.com/questions/293873/do-gravitons-interact-with-each-other https://physics.stackexchange.com/questions/293873/do-gravit... [1] https://en.wikipedia.org/wiki/Color_confinement#Origin https://en.wikipedia.org/wiki/Color_confinement#Origin