Oh, it is true, I am sorry, forgot to multiply the fog term by 'vecFogColor.w' (68th code line of 'Spec.fx').

Code:
float fFog = saturate((camDist - vecFog.x) * vecFog.z) * vecFogColor.w;


Anyway, the fog is activated/deactivated by 'fog_color' variable in liteC.

Salud!