The Opaline mutation is characterised by several features which are invariably present, although many show variations in the intensity of their expression.
In the Opaline these striations are very much reduced in intensity, being almost absent in many individuals, particularly in small birds of yellow (as opposed to buff) feather.
These thumb-prints appear to be associated with a clear 'V', but are now seen less often, since the Budgerigar Standard calls for normal wing markings in the Opaline.
Most Opalines show a brighter body colour than the corresponding non-Opaline, particularly in nest feather and particularly in the rump area.
[5] Towards the end of 1933 Mr and Mrs Ashby of nearby Ayr purchased this 'pied' Cobalt, which they described as being "exceptionally large with a fine head and most excellent spots", although both parents were quite mediocre.
Early in 1936 circumstances forced the Ashby's to dispose of all their Opalines, which at that time were known as 'Marbled', and the entire stock, with the exception of two pairs which went to Andy Wilson of Glasgow, went to Walter Higham of Blackburn,[7] under the care of his aviary manager, Len Hillas.
From these two studs came the vast majority of British Opalines, most of them carrying the wide head and large spots which first caught the attention of the Ashby's.
In Australia, also around 1933 (the exact date is uncertain), Mr S E Terrill discovered a mutant budgerigar, a Light Green hen in nest feather, among thousands of wild birds caught by trappers and sent to Adelaide market.
He bought her, and described her special features as[8] "... almost complete absence of barring on the back of the neck and mantle and its replacement by the body colour ... the mask being extended back, covering the top of the head ... the bars on the wing coverts reduced in number and intensity, their yellow margins being greatly enlarged and nuch suffused in green."
[8] The name 'Opaline' was suggested in 1936 by R J Byfield of Hobart, Tasmania, on being particularly impressed by the vividness of colour shown by these young birds in nest feather.
[8] Terrill adopted the name and after he suggested it in the Budgerigar Bulletin in September 1936 it rapidly gained universal acceptance throughout the world.
In 1962 J Riley of Yorkshire wrote,[9] "In 1930 or 1931 a pair of my Light Greens produced a chick that was of good size and type with mask and spots that were a living dream; the only snag was that its wings were mismarked and grizzled, these markings extending over the bird's back."
The linkage between the Cinnamon and Opaline genes gives rise to two types of split cinnamon-opaline cocks, both visually identical.