Are all garnets naturally red?

No, garnets aren’t only red; they show up naturally in almost every colour you can think of, like green, yellow, orange, and purple. The only tone people do not universally accept for garnets is a perfectly pure, very high-saturation blue, yet colour-shifting blue garnets really do exist.

Even though the deep red pyrope and almandine garnets are the ones most people remember, and they’re usually the easiest to find, the garnet group is a complicated set of minerals. Some types, like tsavorite and demantoid, can give brilliant green tones, and spessartine tends toward vibrant oranges. The whole colour range comes from tiny trace elements, things like iron, manganese, chromium, or vanadium, that were present while the gemstone formed inside the Earth’s crust.