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In addition, frame works in conjunction with other patterns that produce white markings, not on its own. On a horse that has frame but not dominant white, splash, or sabino, the frame will be hidden, only showing up if you color test the horse. In that case you will see the OlwO that indicates the presence of frame and if you check the White Factor you may see that it is large or extensive and notice that the horse has shorter stockings on its legs and smaller facial markings than you might expect.

My experience is that frame does not have much affect on tobiano, and much more effect on horses that are homozygous for splash than heterozygous.

The reason for the fact that Olw appears to have no relation to the common name frame is interesting as well. It was discovered that this was the gene that caused the color pattern that Fallentreefarm described and that used to be called Overo as opposed to tobiano as a paint/pinto pattern. It was also found that breeding two horses with this pattern together could produce an all white foal that died soon after birth from impaction colic. The gene was tagged as "Overo, lethal white," and so the genetic abbreviation was formed. However, the action of the gene shifts the pigmented portions of the horse so that the pigment acts as a "frame" around the white areas, and the term frame was also applied to the gene as a more convenient term.

Some examples of frame in action.

A horse with tobiano and frame. Note the ragged edges on the stockings.

http://www.huntandjump.com/horse.php?horseid=2158995

A horse with heterozygous splash and frame and extensive white factor. Note that the white does not extend onto the belly as would be normal for for the splash without frame when there is that much WF.

http://www.huntandjump.com/horse.php?horseid=2205801

A horse with homozygous splash, frame and extensive white factor. Note the "frame-like" arrangement of the pigment, especially on the top-line.

http://www.huntandjump.com/horse.php?horseid=2256793

A horse with frame, large white factor, and no other white-causing pattern. Note the single small white sock where you would expect white stockings about half-way up the canons.

http://www.huntandjump.com/horse.php?horseid=2436584

A horse with frame and white 2. Note the "frame-like" arrangement of the pigment. White 2 usually causes vertical bands of white on the horse's body.

http://www.huntandjump.com/horse.php?horseid=2446890

Technically speaking, there is a 25% chance of a homozygous frame foal, which will die shortly after birth. However, that does not mean that you can breed two frame horses together three times without getting a lethal gene combination. It means that every time you breed them there is a fairly good chance of a dead foal shortly after birth.

Each parent's code for that site is OOlw or OlwO. The possible combinations are OOlw, OO, OlwOlw, OlwO. You run the risk of getting that third, deadly option every time you breed two frame horses together.