This picture has a yellowback white-breasted orange-headed hen, a normal orange-headed male and a normal black-headed female. If you could see the breast of the normal male in the center, you would see that the purple is much brighter than the female's purple breast the same as the his orange head is brighter than the other female's orange head.
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The Gouldian (or Lady Gouldian) Finch originates from northern Australia where they are currently endangered. In the wild, their head colour would be either red, black or orange; their upper breast would be purple with yellow below and their back would be green.
Many colour mutations have been added by captive breeding and combining the different coloured birds to the different coloured heads gives a large selection for a potential Gould owner to choose from. You really can not go wrong with any of the colours as they are all beautiful.