Not really sure if they are considered heritage or not. I know that they are fairly rare, at least exhibition quality Andalusians anyway. The ALBC lists them as Threatened on the watch list, and provides this info about the breed.
Andalusian Chicken
An ancient and rugged breed of fowl, the Andalusian chickens history is not known; though it is likely rooted in the Castilian chicken breed. In type, it resembles the Spanish chicken, but a pound lighter in weight. Like the other breeds of Mediterranean original it has white ear-lobes and lays a large number of white eggs.
Andalusian chickens were first imported into England by Mr. Leonard Barber in 1846-47. These birds came from Andalusia, about 25 miles from Cadiz, from a Mr. Xeres de la Frontera. In 1851, Mr. Coles of Farnham and Mr. John Taylor of Shepherds Bush also imported more. Andalusian chickens were widely distributed around Cornwall and Devon. The breed was first exhibited at the Baker Street Show, in London, in January of 1853. Somewhere between 1850 and 1855 Andalusian chickens arrived in America.
Andalusian chickens stand high in productivity. It is one of the best layers of eggs, an excellent winter egg producer, has white flesh with plenty of breast meat though the carcass is not very plump, it is an active forager, rugged and hardy. The chicks feather and mature quickly; cockerels will often begin crowing at seven weeks of age. The body type, more coarse than a Leghorn, is easy to produce and maintain.
The chief distinction on the Andalusian chicken breed is the blue color of its plumage. Each feather should be a clear bluish slate, distinctly laced with a dark blue or black. Blue colored fowls are produced as a result of crossing black fowls with white fowls. When two Blue Andalusians chickens are mated together 25% of the chicks will come black in plumage, 50% blue, and the remaining 25% white or splash (white with blue or black splashes).
The best colored Blue Andalusian pullets are produced by mating a dark blue male to a properly colored hen. The best colored Blue Andalusian cockerels are produced by using slightly dark parents of both sexes. There is a tendency for the color to become too light as generations go by. The periodic use of black offspring will repair this defect. The blue ground color should extend down to the fluff.
Andalusian chickens are wonderfully designed for foraging on range. The breeds rugged nature makes it hardy even in cold climates. It does not stand confinement well, however, and is predisposed to feather eating. An excellent traditional cross is an Andalusian male over Langshans females. This produces a hardy brown egg layer that matures early.
The Blue Andalusian chicken was recognized by the American Poultry Association as a standard breed in 1874. Males weigh 7 lbs and females weigh 5.5 lbs.
