Most of the time, the pink is meant as a joke, or possibly a way to trash talk your opponents further (for example, “you just lost to a bunch of pink Posies”).
At the same time, there is something else that calls to painters. Maybe it is the fact that we’ve all had a paint pot of tentacle pink sitting unused among the other paints for the past decade or two, but there is a call to use pink- and to make it appropriate. It might just be the way we’re all ready to be the one to say, “Hey, I can even make this look good.”
The commissar here is something more like that. She wears a light magenta rather than the red that her fellows wear, and overall, I think it works as pink (without shouting “I’m pink”)
The Noise Marines above are an interesting case. The Games Workshop studio color scheme for these guys is bright pink with some black. I’m almost certain it was because someone wanted to pull out their pot of Tentacle Pink and figured he’d never have a better chance than with Slaaneshi chaos marines. Of course, at that point, the objective is to make the color schemes shout out “I’m so pink!”
The last example I’d like to show is something at once more subtle and more brazen than the other two. This is an Iron Kingdoms Infernal Curator. Essentially that means that they’re the kind of demons that make deals for souls.
The pink light sourcing made him use almost the exact color pallet as the noise marines, but the light source touching everything makes for a lot of darker pinks, which in turn make the whole mini look lit in pink light, and not necessarily all dressed in bright hues.