The four recognized colors in Aussies are black, red, blue merle and red merle. You can have self (no copper or white), bi (base color with white) and tri (copper and white) with any of those, but they all refer back to the two main colors, black and red. "Blue" is used for black dogs with merling, as the merle gene gives the coat a "blue" look, depending on the shade and amount of merling present. The base colors should be deep, rich colors, though the red color is often subjected to fading or sunbleaching. Working lines seem to carry more of the deep, non-fading "liver red" the standard refers to.
In this picture (taken by me) you can see Sawyer, a dark blue merle with minimal copper, a black tri and the back end of a red merle. The black and white dog on the right is a border collie mix.
This is a better picture of that red merle. He has rather heavy merling, copper and white modifiers and a blue eye. (photo by me)
Any other color is considered a DQ, although there are also a large number of "yellow" or "sable" Aussies running around, as it's the most common "mismark" in the breed. They used to be allowed and there are pictures of sable tri Aussies running cattle on the old ranches. For whatever reason though, that color was disallowed almost immediately upon the forming of ASCA. Aussies can also throw dilutes (quite commonly) and possess the genes for brindling and ticking.
This is Sunnypup's Sunny, a short-haired yellow. The gene for short-hair is so uncommon! (photo swiped from her profile)
Depending on which registry one is dealing with, the amount of white allowed or desired tends to vary. The constants are that the white must not extend beyond the shoulders and there should be no "body splashes". This is a DQ because of the visual resemblence to MxM "lethal white". Color headed whites, like with Paps, sometimes occur, even in litters born to minimal white parents. Sometimes the argument arises over a pup that has extremely light merling, both in amount and color, as to whether it's a "merle" or "mismark". Aussies carry the "Irish spotting" pattern like Border Collies and Rough/Smooth collies; i.e. white collar, chest/legs and blaze. This is often referred to as "chrome" "splash" or "flash". Some idiot show breeders will cull pups for not being "flashy" enough. They need to be backhanded and barred from showing, IMO.
There are also some interesting coat patterns referred to as "Tweed" and "Harlequin".
Harlequins and Tweeds
This guy is supposedly Aussie/BC; his owner rescued him and his littermate off of Craigslist. I posted him on my Aussie board and there was a big debate as to what his coat pattern actually is. I think he falls under "Harlequin", others said he was just a very interestingly marked merle (photo by me).
Likewise, the copper markings should be confined to "traditional" spots, side of muzzle, eyebrow, minor chest markings, some on the legs. It should not run up onto the body.
The biggest fault of all is "lethal white", which we're all fairly familiar with. It happens when two merle dogs are bred together, producing a MxM dog. These dogs typically have sight and hearing issues, total deafness being very common as well as the lack of properly formed irises and in some severe cases, a total lack of eyeball. Dogs with an excessive amount of white should not automatically be classified as "LW".
Inheritance of Color in the Australian Shepherd is the best site for Aussies and coat genetics. It's really rather fascinating! There is one dog, documented from birth, who went through a complete color change when shedding his puppy coat and ended up being totally white, though without any of the problems normally associated with white. He's under "Coat Changes"
Shalako Australian Shepherd Illustrated Breed Standard_Color is the Illustrated Breed Standard. This site belongs to Shelly Hollen, an ASCA senior breeder judge.
I could go on forever, but I have somewhere to be and I'm already going to be late, LOL!