This is a normal part of ageing for brown shavers and Hy-Line Browns. They become less brown and more blonde as they grow older.
|At two years of age, this girl has become more caramel than cocoa (in real life she looks lighter than this)|
This beautiful friend of mine, for example, was quite cocoa. Then she lost a lot of her feathers in a thorough moulting session over a few weeks, and when they grew back she'd turned into caramel!
The other two haven't moulted as comprehensively, but you can easily tell which feathers are the new ones. They are a now a camouflage-like combination of chocolate and caramel (yum!).
|My two dappled browns.|
Their legs fade, too, becoming fairer and fairer with the years.
So in the same way as you can tell a horse's age by the length of its teeth, you can get an idea of a brown chicken's age by its degree of paleness. Except, of course, that due to natural variation in feather colour, some are pale to start with, so don't go placing any bets on the basis of colour ...