Once a year, Humboldt penguins change all their feathers. Here in Norway, this happens in late summer/early autumn - around August and September.
They are initially white on the front of their bodies with black spots on their bellies, while their backs are completely black. This is a very common camouflage style in the wild, where a number of animals are lighter on their bellies than on their backs. Towards summer, the feathers on the penguin's backs temporarily start to become more and more brownish in colour, and this is a sure sign that they are getting ready to change their plumage. When they are ready, the old feathers will stand out from their bodies, making them look quite "fluffy", and little by little they will fall off. During this time, the penguins will not be in the water as much and their appetite will decrease, but fortunately it only lasts for a few weeks, and they will quickly get their new plumage in place.
The penguin chicks also go through feather changes. One when they are newly hatched, and one when they are just over 1 year old. Then they will go from having the chick plumage to the adult plumage, and get the characteristic dark stripe across the chest and a darker color on the face.