I have seen a lot of dead bodies (military and civilian trauma Dr for decades) and the general pallor rings true, as does the cyanosis. I think the different colour of the neck is a shadow effect. I think this is a real GSW to a real person, not a photoshop, and yes, the heart will keep pumping until the blood all leaks out (and indeed for some time after) - it is autonomous and doesnt stop when the brainstem is destroyed. FWIW, the entry and exit wounds do look consistent with 308 also, and possibly 300WM - take the various youtube reconstructions with a grain of salt, whilst ballistics gel is a reasonable simulant for soft tissue, it doesnt replicate the tensile strength of muscle, sinew and especially bone.