Not sure exactly what you're asking... split wing is a defect in any breed...
As for leg color and other specific breed traits, those are decided when the group of breeders discuss it before the breed is accepted by the APA... a proposed standard is written up and submitted to the APA for approval... once the petition is approved, then the breed must be shown at approved meets in specific numbers within a specific timeframe... once the breed is accepted by the APA, any changes to a breeds standard must be requested through the APA... but really, the APA doesn't make changes... different varieties of a breed may be added going through the whole process once again, but the basic rules of that breed must be followed... like skin color, shank color, ear lobe color, tufts, beard/muffs, comb type, body type, size, etc...