A "texture" isn't limited to one image which gives it some color. Various maps can be used, separately or in combination, by putting them into different channels for each texture. Here are a few examples.

skinmesh

This is the MR-1 head unfolded,
which is used as a template for
the different maps


specular

Specular color: used to define
the color of a highlight on
a given part of a model

luminosity

Luminosity: used to define
the color (if any) seen when
no light is present in a scene
(used to make the lenses appear
to glow in the dark)

alpha

Alpha channel: used to define
which parts of a mesh are "seen"
in a rendered image
(black = visible)

displacement

Displacement: also called a
"height map", is used to create
a 3D visualization from an image



transparency

Transparency: used to define
the opacity of a texture