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Real life
Tiger Eye is a mutation that has been located in Paso Fino horses. The study only looked at a few dozen horses and only from the Paso Fino breed so the mutation may be in other populations as well. The gene called SLC24A5 has three known variants in horses N (no mutation), TE1 and TE2. TE1 and TE2 are different mutations that occurred at different times but happened on the same gene and have effectively identical effects. They are interchangeable but do not stack. (You can have TE1/TE1, TE1/TE2, or TE2/TE2 but no more than two copies in total). Not surprisingly they also discovered that it can have interactions with other eye color affecting genes.

SLC24A5 is a well-documented gene in many animals including humans and can cause ocular albinism (albino of the eye) and is known to produce pale skin in humans.

How eye color works
To understand how Tiger Eye works it helps to understand how eye color works. Eyes really only have brown pigment with some slight variance in shades of brown. Some configurations of pigment cause light to scatter inside the iris in such a way that instead of seeing brown light reflected back at you see green or even blue. The tiger eye gene does not turn brown pigment into yellow pigment. Instead, it reduces the amount of pigment in the eye causing light to scatter in a way that looks yellow. Many genes reduce the amount of pigment in the eye. Famously genes like creme, pearl, and champagne cause large noticeable drops in pigment resulting in a range of eye colors. The more pigment reduction genes active on a horse the paler the eye color will become. Tiger Eye might turn a brown eye gold or an already amber eye to full blue.

Creating
Tiger Eye can now be created in two ways. The Mysterious Sigil herd helper will add one copy of TE1 to a horse. You can also randomly on any create get a copy of TE1 or a copy of TE2. They are both quite rare. It is possible to create a homozygous Tiger Eye horse by getting a random TE1 or TE2 allele as a bonus to a Mysterious Sigil horse. (TE2 is significantly rarer than TE1.)

Purchasing
Both versions of Tiger Eye are now in the GMT lab and can be added to any foundation for 5GMTs, or added to a lined horse who missed it for 1GMT.

It can also be purchased with USD for $5 per copy. It will be available until the end of June. After that, it will go into the normal random gene sale rotation.

Sharing
Tiger Eye is a publicly available and open gene with no license required.