To me it looks as if on the left side, towards be border of the smoke where it gets thinner, i.e. the density goes towards 0, it turns to black.
I cannot exactly reproduce it, but a similar effect can be achieved if you plug the Density output of the Volume Info node into the Color ot the Principled Volume and use a Color Ramp inbetween where you move the black slider from the left in to color the less dense borders with black.
In my example I also made it a bit pinkish red as it it seems in your example, maybe you can even use the density info for some emission. My answer is more a general idea of what you can do to get more stylized smoke, not a finished replica of the reference.
