Edit: The colour of any Qetasi is debatable. Instead of being confined to the "Pelt Colour Gradient", you are free to use any shade of brown (red-brown, orange-brown, desaturated brown, etc). Eye colours will, however, remain within the limits of the gradients seen on the species sheet.

Cervequus qetasis
Qetasi (Keh-tah-see) Emphasis on "tah"
Plural: Qetasin (Keh-tah-sin)
Descriptive: Qetasian (Keh-tay-zhin) Emphasis on "tay"

I. Appearance
A. BODY STRUCTURE
The Qetasin are a deer-like species with visual elements from horses, lions and other ruminants. They share similarities with Unicorns in these aspects, but they are not related otherwise.
Their bodies are slim and rectangular, with long, tapering legs that are commonly seen in deer. Their hooves are cloven, and accompanied by two dewclaws on each leg. Ears are large and leaf-shaped. Their faces are primarily horse-like in appearance, but the proportions are more like a deer’s in that they have broad foreheads and short, small muzzles. Tails are structured like those on horses. Feathering is possible and can be as heavy as the creator desires, but it remains a noticeable trait of Qetasin that live in colder environments. Regardless of habitat, males often grow manes that start just behind the head and extend onto the belly. Beards usually accompany the manes.
Horns and antlers are more likely to vary from one Qetasi to another. The five types are illustrated, ranging from simple antelope horns, to antlers with multiple prongs. Ridging can occur, but for simplicity’s sake the illustrations depict only the basic horn structures. For reference purposes, look up: oryx, Kudu and whitetail deer. (Horns are always the same colour as hooves, and Antlers are always a light tan.)
Qetasin can also have feathered wings, though the current depictions are wingless.

B. COLOUR
Qetasian coats are any shade of muted brown, as seen with the Pelt colour gradient. White and black are only possible if the parents carry the recessive genes, which are limited to parents who are either dark brown or desaturated peach. Their underbellies are white, regardless of colour.
Eye colours can be any shade of green, blue or brown (refer to eye colour gradients). *See "SIGHT" for more information.

C. MARKINGS
Markings vary greatly, but are either striped or splotched (unless they are vein-like extensions of the white underbelly). The colours are still within the pelt gradient, but white and black are also allowed. Any colours outside of the pelt gradient (red, yellow, blue, green, etc.) are limited to small markings on the wings, if your Qetasi has any.
*See "SIGHT" for more information.

II. Senses
A. SIGHT
Qetasin possess colour processing that is more limited than a human's. However, they have superior nocturnal vision.
Unfortunately a Qetasi with lightly pigmented irises is likely to suffer from light sensitivity. As this Qetasi ages, the sensitivity has a higher chance of turning into blindness or blurred vision. *Qetasin with lighter irises and dark markings beneath the eyes are less likely to develop blindness.

B. SMELL
Qetasin use their senses of smell to distinguish one member of the herd from another, and can easily detect predators if they happen to be upwind. This combination makes smell one of the more important senses to a Qetasi.

C. HEARING
Their large ears provide Qetasin with adequate senses of hearing, which ranks second to their senses of smell.

III. Society
-Qetasin travel in matriarchal herds, allowing the presence of males only during breeding season or if they are younger than five months.

A. COMMUNICATION
Body language is the primary means of communication between Qetasin, which makes vocal usage unnecessary after a certain age. Emotions are expressed with the ears, pose and tail. Perked ears are a sign of alertness or interest, the former usually combined with an upright, stiff pose and widened eyes. Relaxed ears signify contentedness or calmness, and flat ears signify annoyance, anger or disinterest. The tail thrashes when annoyed, but perks up when the Qetasi is feeling particularly flirty or wary.
During childhood, a fawn may make high-pitched noises to express its emotions. This may decrease over time, though some continue to use a short chirrup as a greeting.

B. SEASONS
Breeding season begins after the first frost and lasts until early winter. During this time, wild Qetasian males will fight for a position in the herd until they've met a ratio of one accepted male per three females.
Birthing season begins when the ground thaws and the plants start budding.

*The information regarding Qetasian societies is limited to wild herds. Captured Qetasin are likely to develop different behaviours.

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TL;DR

Really, though, you don't have to be as picky about these things if you decide to create one. Just be sure to stay within the colour limits.
In regards to white/black Qetasi, you'd have a 25 percent chance of receiving a white/black Qetasi if you bred two parents containing the recessive genes, and a 50 percent chance if you bred one white/black parent with another that possesses the recessive genes. Nooo, technicalities! But for the sake of fairness, I'd appreciate it if you didn't start out with a white or black Qetasi.

Let me know if you make one. I'd love to see what people come up with.