They did change as their feathers grew in but the lighter one did stay light & the darker ones actually got darker. The ones that seems to change a lot are reds with blue or dark grey. One actually started as a very dark chick & grew in lovely speckles reddish tone, eventually molting to turn gold, what a surprise! When they go through molt, some may change again.
Let me find some pics of the hen I call Mystery, not even sure of her breed...she is not an Olive Egger, she lays a gorgeous creamy, pale tan egg. Her feather colors were such a change, it really is cool how they can develop various color feathers.
She started as a dark brown fuzz with cute reddish gold fuzzy face, then gradually the dark fuzz disappeared as reddish gold feathers grew in. Then her molt was more gold! Mystery is such a sweet girl, too.
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You can still see some dark color on the edges of her feathers. So pretty!