The photographer, David, was startled to see this rosella and managed to lure it back with food to get a photograph, recognising it was very different to a normally coloured Crimson Rosella
This is an unusual Crimson Rosella and from what I can gather, is a result of a genetic mutation, specifically a dilution or white mutation, affecting the bird's plumage colour. It's most likely caused by a recessive allele that reduces or eliminates pigment production (in this case red), resulting in a white or pale-coloured bird. It's likely that a combination of dilution and recessive mutations are responsible for the white colour.