Got this answer from top canary man...short but sweet hope it helps.

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I thought that my self to be honest just i have never bothered with colour feeding etc i am finding it really hard 2 get a pair tdh thank mate

The trouble with colour feeding is unless you feed an equal amount throughout the moult you end up with different shades in the feather as it grows and then if they lose a feather and regrow one that one has its natural colour

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Yea i understand what your saying mate. I have a opel hen and was wondering if was to feed here some source of white colouring would it take away her speckles off yellow. Myt give it ago for a chage lol