Scientists can use the color of minerals to tell them apart.
Idiochromatic minerals (self-colored) due to their composition. The color is constant and predictable.
Allochromatic minerals (other colored) due to trace impurities or defects in their structure. The color is variable and unpredictable.
Pseudochromatic minerals (false colored) due to effects produced by light. The color is variable but a unique property of the mineral.