I'm looking at this particular thread: www.renderosity.com/mod/forumpro/showthread.php

.. which should get me started on what I wish to go about. But what I want to know is whether I can throw displacement on a higher layer, no displacement (just bump) on the lower ones. Is that even possible?

Just so you know what I have in mind, I'm thinking of possibilities for body hair without adding a prop or figure, just a displaced layer. Is that doable?

Displacement works on the underlying geometry of the surface, not on any one texture layer.

It's a mistake to think of blended textures or colours as separate layers in the final render. No matter how many layers of texture you combine in a shader, there is only one surface with only one final colour value for each rendered pixel.

It sounds like you need a bump or displacement map based on the hair texture map, with the hairs as lighter strokes against a black background.

Displacement moves the mesh, it doesn't create a layer above or below the mesh, so no it's not possible.

Further, as Izi says, each point has one color (and one position, and one normal). If it appears to have more than one color, that's just your brain interpreting it that way.

Thanks, both of you... it seemed like it wasn't possible by my experimenting, but it's nice to know I wasn't just missing something. And experimenting usually isn't a total waste of time... you usually learn something....