My sister sent me this recently and although we grew up with zebra finches in our backyard aviary neither of us have ever seen a blue mutation. Could this pic be photoshopped?
This site mentions the 'normal blue' mutation.
Could it just be a juvenile colour that will grow out? I know I have heard of rabbits being born blue.
'Normal Blue' is a mutation that produces grey markings rather than black. (Like the blue cattle dog it isn't really blue)
I don't think Zebra Finches have a gene capable of producing blue feathers unless it is a hybrid.