There is no standard location for expiration dates for unopened hair dye products. While different manufacturers sometimes list freshness or best used by dates on their products, not every company does so.
The government does not regulate expiration dates on hair dye. Unopened hair dye products stored in manufacturer-recommended conditions have a very long shelf life. However, once the product is opened and exposed to air and light, it should be used according to the manufacturer's recommendations. When hair dye products are mixed for use, they should be used immediately or discarded. Don't reuse or store mixed hair color products.