FAQ: Does a dark factor affect the colour of SL ino green (lutino) Agapornis roseicollis ?
The dark factor is an autosomal incomplete dominant mutation which causes a change in the feather structure. This mutation modifies the width of the spongy zone in a feather of the structural type.
In a normal green bird, the ‘white’ daylight hits the barbs of the feather and that light is partially absorbed by the eumelanin granules in the barb’s core (medulla). In the spongy zone, there is a reflection of these light waves through the hollows present. This creates a blue light. The vacuoles present in the feather’s medulla cause the blue light to be reflected outward by the cortex containing the yellow pigment. The combination of the blue light and the yellow pigment in the cortex creates the optic colour green
With a dark factor, in this modified spongy zone ‘dark blue’ light is created through interference instead of the (lighter) blue light which is normally created in the spongy zone of a green wild type bird. The vacuoles reflect the darker blue light through the cortex containing the yellow psittacine. The combination of dark blue and yellow gives an optically darker green colour: a D green bird. The presence of a second dark factor decreases the width of the spongy zone somewhat further, and thus will increase the effect even more. The result is that the bird is DD green. Because the dark factor is caused by a change in the spongy zone in the feather, this mutation can only be found in feathers of the structural type.
In contradiction to a normal green, a sex-linked ino (SL ino) has seriously deformed and underdeveloped melanosomal matrices in the medulla of the feathers. The melanosome matrices formed are black, but they are seriously deformed, too small and there are not enough of them to absorb light and create a blue colour in the spongy zone. That is why we only see the yellow colour of the psittacine in the structural feathers of SL ino Agapornis roseicollis.
Due to the absence of eumelanin we expect that the rump colour also will be white, but in Agapornis roseicollis we see a blue shade on the rump. That is the effect of the presence of these small deformed melanosomal matrices in the feathers of the rump. (The green shade in the yellow feathers of SL ino green budgerigar is also caused by these deformed melanosomal matrices).
If we combine a dark factor with SL ino, the dark factor will modify the width of the spongy zone, but due to the absence of normal eumelanin in the medulla, it will have no effect on the yellow colour. It will only create a darker blue shade on the white rump feathers. In combination with two dark factors (DD SL ino) the blue shade on the rump feathers will be stronger.
The red colour of the mask will remain unchanged even with the presence of one or two dark factors, because the mask of A. roseicollis is made up of feathers of the ornamental type (without a spongy zone) and these are only filled with red psittacine (under normal circumstances).