Generally before lighting or texturing, colour all objects the same- usually about 25% grey. This will allow you to see unbiased contrasts and values of the scene.
Ambient Colour – The environment colour- reflective surfaces will reflect the ambient colour. for example- in the real world the ambient light is usually the colour of the sky.
Diffuse – The actual colour of the object. No shadows or highlights- just flat colours.
Specular Colour – The colour of the reflection (Eg for the rainbow colours coming off an oil spill, create a specular colour map.
Specular Level– Where and how intense specular highlights are. Black = 0% White = 100%
Glossiness – Similar to specular level- black and white determines how glossy an area is.
Self Illumination – These areas glow through shadows- LCD screens etc. Glow will need to be added in post.
Opacity – Determines what part of the map is transparent and opaque- useful for wire fences, grills etc. Usually needs a bump map to add depth, and a specular map to prevent transparent areas from reflecting.
Bump – Give the impression of texture on your object. Black sinks in, white sticks out. Handy to start from a neutral 50% grey Light bounces off as if there is more geometry on the model.
Displacement – Similar to a bump map, but actually physically moves the pixels of the object. EG- On a sphere, there will still be a smooth edge on the spherewith a bump map, but a displacement map will affect the geometry of the object.
Normal Maps – A type of bump map, but better resolution and better lighting results. Popular in games. Can be applied with a separate bump map, which is handy