The juvenile plumage initially develops with the head and upper parts becoming more ginger-brown. Its first moult (post-juvenile moult) usually starts after the bird first flies [check out this link] when just the head and body feathers will be renewed.
This is a 1st winter bird still showing the retention of some of its juvenile feathers including the dark tail but with the distinctive black tipped yellow bill. Through its first summer it will hold onto some of the faded juvenile plumage but may acquire a partial dark hood, often heavily spotted white, plus the legs and bill base will change to a more orange-red.
Above is an adult in its winter plumage sporting the bold dark ear spot and black tipped red bill. Its spring moult is also a partial moult when only the head and body feathers are renewed.
At the end of the its two year moult cycle this years juvenile (image 1) will look much the same as its adult parent showing that distinctive dark chocolate-brown cap plus the red bill and legs. FAB.