Lighted Coffee

Lighted Coffee
What makes coffee with skim milk darker than coffee with cream?

When cream is added to coffee it turns it a very light tan color. When whole milk is added it lightens up the coffee to a light brown. When skim milk is added the coffee barely changes from black to a dark brown. The only idea I have is that maybe the fat in cream reflects different wavelengths of light. But if that was the case wouldn't milk and cream appear to be different colors when isolated, as opposed to just opaque white?

cream is much thicker than skim milk.
if you kept adding milk youd get the same color in the coffee as there is in the coffee with cream.