If you breed a visual to anything, all the offspring will be hets.
If you breed a het to a normal, or another het, then all of the offspring will possibly be het. There is no definite way to know which ones are het and which ones are not. Some of the het pieds may have a het pied maker, which is two solid black lines that are each side of the snakes belly near the tail. Here is a picture of the het pied marker:
Hope this helps.