The Registry defines markings as configurations of solid white hairs contrasting with the surrounding coat color. This distinction is particularly important on grey horses which grow lighter in coat color as they age, often disguising white markings.
Pink skin is a permanent identifying mark.
If your horse is grey you must complete boxes for underlying pink skin on the markings form. Pink skin is easier to identify if the coat is wet or shaved. When you draw markings, secure your horse in front of you so that you can get all of the details. Don't try to do it from memory. Do not draw black points on a bay horse.