What types of units are usually assigned colors in the same color family, such as different shades of blue?

Question

a. geologic units of similar ages
b. geologic units of similar colors
c. geologic units of similar types of rock
d. geologic units of different ages

Answer 1

Similar ages.

Rocks that might all fall in the Ordovician might all be different shades of one colour depending perhaps on type and more specific age.

Answer 2

depends on the map, but the most common practice, in larger scale maps at least, is the use of colors to indicate similar ages. When one is dealing with a small scale map where most of the rocks are of similar age anyway, the use of colors to correspond with rock type is more common.