These brightly coloured egg boxes (recycled fibre pulp) are certified as food safe for the transportation of eggs under EC Regulations. Food-safe here is qualified as food that is wrapped and not in direct contact with the container, like an egg, which is contained within an egg shell. It does not mean, for example, safe for unwrapped cakes or chocolates.
It should be noted that you should not leave or store coloured egg boxes in direct sunlight as they will discolour. The process of colouring fibre egg boxes does not allow a dye fixative to be used so they will fade if left in direct sunlight or bright daylight.