why do my eyes go from grey to blue and sometimes even a light purple

Answer 1

Dark eyes are dark because of a pigment made in the iris called melanin. Lighter colored eyes have less melanin with blue eyes having the least amount. Generally, the amount of melanin in the eye remains constant, but it can change over time depending on the environment and individual (some people are born with a certain eye color that changes as they age). More acute changes are likely due to the light in the environment and not the pigments in the eye themselves, since, for the most part, the amount of pigment remains constant throughout adulthood. Therefore, your question is mostly a physics question and not actually a genetics question, since you would need to understand the way different wavelengths of light in your environment interact with the pigments in your eyes.