Belongs more on the main Painting and Modelling Forum but pretty much what Cadichan said. Mine even look like the Bloodletters at one point when I do them
Prime Black
Basecoat Scab Red
Drybrush several coats of Blood Red in order to lighten it up progressively
Once it's pretty much like the Bloodletters start drybrushing a roughly 3:1 mix of Skull White to Blood Red over the top.
Pick out teeth and claws with Bleached Bone
Wash Bleached bone with Sepia
Drybrush Bleached Bone sections lightly to brighten them up again
Pick out eyes with Golden Yellow
Each eye gets a small vertical line of Chaos Black to form the pupil rather than the usual dot
Inside of the mouth and tongue gets a thin coat Scab Red
As for the fire as the Army Book says they throw pink fire it was just painted white as the entire model is painted up following the steps, they lightly drybrushed towards the top with the pink mix.
Need pretty thin coats though. I had to do it this way as I had no red wash or pink paint
Finished result
Might make a proper tutorial for them later.
I think the first one you mentioned should turn out pretty well. Also It's Tzeentch so they're not meant to be uniform so might as well try out both of them as a mix of various shades of pink would probably suit them more.