How do you add roasted flavour to it afterward?
I'm the opposite. I only make brown stock--for its intense flavour. I only make white stock when I'm too lazy too roast the bones.
In many of the places I worked at, chicken stock was never made with roasted bones because we wanted a neutral flavor. If we wanted a stock with roasted flavor we'd use that neutral stock and then add roasted bones to it. On the other hand veal stock was always made with roasted bones.