RED-ON-BLUE TABBIES & PSEUDO-CINNAMON
Colours can be modified by numerous genes (known as polygenes) which creates warmer or cooler tones. Marjan Boonen, a breeder in The Netherlands, has noticed that red cats sometimes have a bluish hue on their extremities: tail, feet, muzzles and ears. In many cases, kittens with bluish extremities turned fully red as they grew older, but some adult cats still retain the blue/grey hue. Tosca, a solid red female shows really clear bluish hues while the red-and-white bicolour housecat shows the blue tailtip really well and the lighter part of his tabby pattern also looks a bit grey. In black/brown tabby cats, polygenes are known to affect the background colour, sometimes warming (brightening) it and sometimes "cooling" it. In silver cats, there is sometimes a golden "tarnish" on the muzzle. In red or cream cats (the red/cream colour is due to phaeomelanin) the bluish effect may be due to such genes causing some eumelanin to be expressed. Because the bluish hue is retricted to the extremities (points) it may be affected by temperature, as those regions are cooler than the cat's torso.
Here are some photos of an unusually coloured 11-month-old household pet called Oliver (owned by Jill Bristow) shown in ACFA in Canada in 2015. He started off as a dark orange tabby feral/stray kitten caught in a squirrel trap when he was about six weeks old in Winnipeg. He then darkened as he has got older and to a deeper orange brown colour which has a slight bluish undertone. It definitely looks much more brown than a normal red tabby and resembles the cinnamon colour (a recessive allele of Black i.e. a eumelanin colour). Howeve Oliver DNA tests as B/B and non-agouti meaning he should be self black (if no O gene is present) or self red (if the O gene is also present). As he is not black, he must be genetically red. He is not chocolate or cinnamon (alleles of black), despite the visual appearance. It's as though the red gene doesn't fully suppress the expression of eumelanin. He carries colourpoint and blue dilution. Non-agouti red usually shows ghost markings, but not on a blue background. The blue undertone is the unknown factor that might be a novel mutation tht modifies the base colour of red.
(2016) Polly McNichols sent some photos of two male tortie littermates, Edward (pictured as a kitten and an adult) and Rocky (who was adopted, so only shown as a kitten). Edward was 18 months old at the time of the adult photos. He's a pale orange tabby and has one grey tortie paw and lower leg. His mother was a feral black and orange tortie and his dad was a feral pale orange tabby (both parents are now neutered). His blue markings could be due to a skin cell mutation (like a birthmark). Since all the litter were orange or cream (4 males and 1 female), he can’t have swapped cells with a darker sibling in utero. His overall coat colour is interesting. He has a dusty blue hue to his fur. The first time he went to the vet the vet tech commented that it looked like someone had sprinkled dust all over him. This resembles an effect dubbed “blue ginger” where not all eumelanin is converted to phaeomelanin. Unlike most blue gingers reported, Edward’s doesn’t have bluish face, tail and paws. He just has a mottled left front paw and some bluish spots on the back of his hind paw, plus a little at the base and tips. His littermate, Rocky, had a definite bluish grey hue to the end of his tail, hind paws and legs.
In January 2017, Anita Cheetham mentioned a British Shorthair red stud who regularly deposits a black spot on a paw pad on a lot of his kittens. She had recently had a kitten from him that had black hairs just on a back foot. In addition, some of the red girls' noses go grey and the nose leathers go quite black (the atter may be lentigo or black freckling, which is not uncommon on red cats).
Chart: Recently Noted Mutations of Red Pigment
These colours are under investigation and may not be true mutations, just slight modifications of how known genes are being expressed visually. For now I'll use the term "mutation" in a very loose sense. All of these occur on cats that are genetically red. The colours visuallyb resemble eumelanin (black pigment) colours even though no black pigment is present. One mutation/modification turns red pigment into a rich cinnamon colour. Another turns the ground colour of red tabbies to a bluish/lilac colour. This may also be responsible for the bluish tones at the extremities of some red cats.