The Aspect

The colour of ambergris varies from black, through dark brown, through light brown to yellow/gold or even grey. The colour tends to lighten with time.
Most frequently, good quality ambergris is a dark to light chocolate colour.
Sometimes, a grey/white, powdery crystallisation is formed on the surface.....often in uneven patches.
The texture is granulous. The "kidneys" have a tighter and finer texture than the layers or strata.

Here are some pictures: