I put my guestion here instead of "The Engine", since it is most probably a noob question.

My problem is: I currently test bump mapping via mtl_SpecBump and though the effect is quite nice, it seems, the surfaces ignore the color values of the light. (See the screenshots below, please.)

What am I doing wrong?

We can see a color change between your two screenshots.
Read the manual, i think Ambient map and sun map properties affects your shader ?
Do you have place the normal map on second skin ?
This is the alpha of 2nd map that is taken account for specular if i remember well ...

Maybe changing the emissive and ambient colors in the material might help. Give it a try.

@Ratchett:

It's not a model, it's a BSP-Brush. So no Skins, just the required Wood.tga and Wood_n.tga as texes. Sorry if that wasn't clear.

@3run;

Tinkering with the specular values in mtlFX.c just renders it red or whatever I change, totally unimpressed by ambient light. I am currently tinkering, however with ambient_blue etc. and this seems to at least point in the direction of the desired result. So maybe you fixed my problem, thank you (at least you gave me something to try ;)) Still tweaking, however.

If anyone wants to suggest something different here, I'll be all ears.

If you upload a test level (including textures and code) I can have a look at it tomorrow.

That is a very generous offer, and I feel impolite declining it for now. I just feel it will be better if I claw my way through this by myself to learn. May I come back to you if I fail and start to cry?