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m
 White
White is not a color; white hairs are crystal clear and colorless
WHITE hair looks that way because it's as clear and colorless as
pure water. Snowflakes are made up of clear, pure water in
the form of ice, yet appear to be white. In the same way, when the light hits clear,
colorless hairs, they appear to be white.
Very diluted hair, which can sometimes be mistaken for white, has
a
certain amount of pigment
(color) distributed inside each hair.
WHITE hair occurs when the pigment-making cells are turned OFF.
This can happen before birth, so that the horse is born with
pigment-free areas (born-white hair), or it can happen later, so
that only individual hairs have no pigment (acquired white hair).
White hair as it relates to skin color: sometimes the skin
under white hairs has pigment in it, and sometimes it doesn't.
It depends on the type of white hair pattern in the horse's genes.
WHITE AREAS vs. ROANING
The various known patterns of white hairs may cause entire areas
to be pigment free, as in the large white "spots" of a tobiano, or
individual hairs to be pigment free, as in the scattered white hairs
among the dark in parts of a rabicano pattern.
This web site will use "white areas" when
discussing the former, and "roaning" for the latter,
with this caveat:
... apologies for the possibly-confusing terminology:
there is a specific gene called roan. The roan gene
causes a specific type of "roaning". However, not all
"roaning" is caused by the roan gene; i.e. not all roaning is
roan (see roan and the various other white patterns for more
in-depth explanations.)
You can choose a button, below, to begin learning about any one
of the white-hair patterns present in horses.
         
Factoid: The various patterns of white areas seem to have arisen as a
result of the domestication of horses, as happens with other mammals.
More in-depth information about white hairs and the underlying skin:
Pigment can be turned off from birth, to an area, as in the case of white
markings; or to individual hairs, at varying times in the horse's
life, by various roan-like patterns; or the pigment can be turned
off gradually, to most of the horse's hair only (not the skin), by the
prematurely-graying gene ("gray").
In the first case -- a star, a stocking, or other pinto (or
"paint") patterns - pigment is also absent from the skin out of which
the hair grows. This is also the case under some appaloosa
(leopard complex) patterns, and with some roaning. However, in many roan-like
patterns, and as a gray horse loses the pigment in its hairs, the
skin itself has normal pigmentation for whatever color the rest of
the horse is (or was).
The pigment in the skin of a graying
horse sometimes also later disappears in patches, causing
pink-skinned patches, usually small ones, and usually most
noticeably on the face. This is called gray depigmentation,
and is similar to vitiligo in humans.
"Roaning" is one way to describe areas where there are white
hairs mixed in among colored hairs, like salt-and-pepper. Some
white-area genes cause areas of roaning, and under that type of
roaning, varied amounts of pigment-free skin may be present.
In the white-hair-causing pattern called rabicano, for example,
there may be some pigment-free pink skin under the white, even
though it's popularly considered a type of roaning; and when the
sabino pattern causes roaning, pink skin may also be present under
the "roaned" areas. The differences between the specific
pattern called roan, and the ones that cause "roaning", will be
explained in their own sections.
A quick look at a white-spotted horse:
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Does the white look:
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POURED ON (smooth edges) from above? Think
tobiano.
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SPRAY-PAINTED ON (jagged edges, lacy, or
roaned) from below, beginning with the feet and face? Think
sabino.
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SPRAY-PAINTED ON (jagged edges, or lacy) the sides of the body
and on the face only? Think frame.
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like the horse was DIPPED in white (smooth edges) from
the feet up? Think splash.
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