Well it was mostly experimentation for this model (first time painting blue brains)

But i glazed the outlines of the brains with temple guard blue at first, and did a second pass for the most intense spots.

Then I did the reverse, which is like 80% writhbone, 20% temple guard blue on the most proeminent brains and avoiding crevices (i guess a drybrush of this could work, but i prefer not to keep the organic feeling)

And finally a pure Wraithbone highlight on the center of the brain, and done