It is the underlying mutation of the Danish Pied variety, aka Harlequin.
[3][4] All pied budgerigars are characterised by having irregular patches of completely clear feathers appearing anywhere in the body, head or wings.
Such patches are devoid of the black melanin pigment and show just the ground colour—yellow in green-series birds and white in blue-series.
In the Recessive Pied the clear areas are very extensive and many Recessive Pieds are predominantly clear with quite small irregularly shaped areas of normal pigmentation.
As with all pieds, there is a large variation in the position and extent of the variegated patches, but the typical striations are almost always present around the eyes.