The Isabel mutation first appeared in green stock. The Isabel is the term used to describe the dilute version of the brown. As with the agate, the effect of this mutation is to reduce in width the brown striations within the feather. It must be noted that although the striations are reduced in width, this does not refer to a dilution of melanin colour, as we still require the same depth of eumelanin brown in the intensive Isabel as the seen in the classic brown. The ideal specimen will display well defined and spaced chocolate brown colour striations, unbroken in length. They should be present on the head, back and flanks, extending into the chest area. The ideal intensive Isabel will show no phaeomelanin brown on the tips and edges of the feathers. The underflue is a paler version of the brown. The eye colour of the Isabel in nest feather is bright red and tends to darken as the bird matures. The horny areas, beak, legs and feet, will be flesh coloured. It is wise, wherever possible, to pair Isabel to Isabel to maintain the dilute striations to perfection. It may, however, be necessary every three to four years to introduce an agate as one of the breeding pair to endeavour to maintain the dilute striations, as the continual pairing of Isabel to Isabel will no doubt lead to a deterioration of the melanin markings. It is not recommended to pair Isabel to brown as this will lead to intermediate quality birds being bred. The Isabel offspring produced will not be good Isabel’s as the birds will display an in between melanin width. One should only contemplate this style of pairing if you are commencing a controlled experimental breeding programme and then only when you have sufficient experience to do so. As with the agate, we now identify the Isabel not as a dilute but by its recognised term of Isabel. This is usually prefixed by the feather type and lipochrome ground colour, e.g. intensive red Isabel, non intensive red Isabel, etc. The Isabel is available in all ground colours and follows the sex linked inheritance pattern.
This article is taken from the coloured canaries’ guide of the CCBA.