I imagine the pink portions are white, the iridophores should always yield blue/green right? Although pink should just be all colors present with some extra red.. so maybe some red chromatophores are "firing" along with a good deal of leucophores? I guess the only other options would be pink ambient light or more likely something digital.
I tried comparing the color to the surround landscape to see if there was a digital affect in play and everything I saw looked appropriate (the reds, oranges and purples looked as I would expect and the browns had no pink cast). The male looked like he had coraline algae growing on his mantle but I don't think that is possible.
It's not bioluminescence. So it could only be coming from the surroundings. I suppose what you are asking is if it's pink light reflecting on non-pigmented leucophores or white, full-spectrum, light shining on a combination of chromatophores to yield pink coloration. And I think it's improbable that it is pink light being cast.
I have no idea whether or not it would be possible for algae to grow on them though I would also expect not. Regardless the pink coloration seems to come and go. As far as digitally, I think it would be rather easy, with some good software, to do this, but I don't really see any motivation.
So I'm gonna say I think it's most likely leucophores and red chromatophores.