Why do crystals, like quartz and diamonds, form in different colors?

Question

Some crystals, like quartz and diamonds, form in a variety of different colors. For example, quartz can be clear, 'foggy', pink, yellow, and even blue. - What happens during the crystal's formation to make it one color or another?

Answer 1

Trace elements can color minerals. Add a little of mineral X, and you have a blue diamond. Mineral Y and it's red.