Final answer:
Minerals receive their color from chemical compositions or trace impurities. Transition metals create colored complexes due to d-orbital light absorption. Streak tests show true color by powdering the mineral to reduce impurity effects.
Step-by-step explanation:
The color of minerals is influenced by their chemical composition and the presence of certain elements, which can alter the color in significant ways. For instance, in idiochromatic minerals, the color comes from the essential components of the mineral itself, whereas allochromatic minerals like ruby owe their color to trace impurities, such as Cr³+ ions substituting for Al³+ ions in corundum, resulting in a deep red color.
Additionally, the colors of transition metals complexes, like malachite (green), azurite (blue), and proustite (red), are impacted by how the d-orbitals of the metal atoms absorb light of various energies. In the process of streak testing, the color of a mineral in powdered form might differ from its appearance in hand-sample because impurities have less effect on light absorption when the mineral is powdered.