Discoloration usually happens when your Philips Avent parts are exposed to food containing dyes or colorings that stain plastic, like tomato sauce and certain green vegetables.
To avoid discoloration, keep parts separate from food, containers, and other objects containing food residue during cleaning, disinfection and storage.
Discoloration is also caused by exposure to leftover residue from previous washing/cleaning sessions, specific cleaning agents, direct sunlight and calcium buildup from washing the parts in hard water.
Please follow your Philips Avent product's recommended cleaning, disinfection, and storage instructions to avoid discoloration.