There are many Dun Factor points, below are the more common points.
Ear Tipping / Ear Edging
Face Masking Mane / Tail Frosting
Click the link below: For interesting information on characteristics on hair coat patterns and colors.
The calculator will give you the possible coat colors and their probabilities when given the parents coat color and pattern information. Calculation accuracy of the offspring color possibilities and probabilities can be greatly increased when providing the color genetics
of the sire and dam.
Gray is one of them exceptions and is explained on the site.
Click the link below for interesting information on coat colors calculations.