I think I figured it out! Yesterday I bought a few back issues of White Dwarf, including May 2011, which has a feature on Tomb Kings. In there was some nice painting info, including a rather striking crimson warsphinx.
Looking at it, it bore a very striking resemblance to the Obsidian Rose armor coloring. Now, I had to use the paint comparison chart since the tutorial was written using the old color range. But I did it on a couple of Scourges today and it looked amazing! I still need to add some final highlights, but I think that tutorial nailed it!
Here's the basic info:
Start with a black basecoat, and do your initial edge painting with Khorne red.
Give it two heavy base coats of Carroburg crimson.
Then do edge highlighting with a blend consisting of equal parts Mephiston red and Evil Sunz scarlet.
Finally, apply your finishing highlights with troll slayer orange.
This looked really good over the Kantor blue bodysuits I painted my Scourges wearing, and I think I've about nailed the effect. I'll have to try this on Hellion skyboards next!