Variations of the Koolie are determined primarily by coat color. (It again should be noted that coat color is not merely a visual thing; it can indicate health problems.) Variations on a lesser level are also recognized via coat lengths as well as are ear styles.
There are many merle variations (preferred color) as well as a few solid colors. The Koolie has more merle variations than most dogs, and they are black, blue, chocolate, fawn, gray, lilac, liver, red and tan. The solid colors tend to be far fewer, with black being one and white being another — this latter solid being the worst. Why is white the worst? you may ask. It's a result of merle-merle breeding that indicates a distinct possibility of blindness and / or deafness. White Koolies are not always blind or deaf, but it is very possible they can be. Due to this, breeders are beginning to accept solid coated Koolies when previously they were considered less desirable.
As for the lesser variants, coat styles include short, medium and long hair, single- or double-coats and smooth or rough hair. (The long-haired Koolie is not rare but it's not at all that common either.) The ears are another variation that should be noted: dropped (i.e., droopy) and pricked (standing) ears. Since most people who have these dogs are graziers and drovers, these seemingly cosmetic variations are extremely important and as such, some are favored over others.