The most common pre-eruptive staining is:

Intrinsic colors are determined by optical properties of enamel and dentin and their interaction with light. If incorporated into the dentin, they become visible because of the translucency of the enamel. They can be related to periods of tooth development, as in amelogenesis imperfecta  or dentinogenesis imperfecta or they may be acquired after completion of tooth development, as in pulp necrosis. The most common pre-eruptive staining is endemic fluorosis caused by excessive fluoride ingestion during tooth development.