Tan markings

Tan markings in dogs are actually nothing but wolf (grizzle) markings, but where the colours of the coat are a bit more extreme, giving the impression of a dark base coat with paler markings. A lot of people are quite uncertain on where tan should appear, and tend to put them in here and there. But when you know what the markings should really look like, they become easy as pie to add onto any dog!
The traditional wolf markings are found on the underside and sides of the muzzle, above the eyes, inside the ears, under the chin, on the chest, on the paws and lower legs, on the insides of the legs and under the tail. In dogs, we have different types of modifier genes, which means the pattern can look rather different from that! 

Different amounts of tan

This is an example of a dog that has very minor markings. When a dog is marked like this, we normally have genes at work, that help make the pattern less spread out. There is also a masking gene that you will sometimes see in black dogs with tan markings. This gene can't be found in all breeds, but you can see it in for instance australian shepherds, german shepherds and american cocker spaniels. If we broke down the genetics, we could say that this dog is black + a tan marking gene + a tan modifier gene + a black mask gene. If the dog was longhaired, you might see even less tan on the legs (since the upper black fur would cover part of the feet).
There is one marking, however, that always stays - even if the rest of the dog is solid coloured, if it has tan here, it IS tan-marked! What I'm talking about is the marking around the vent! Not to be confused with a tan tailtip - if you look at a real wolf (remember, tan markings are wolf markings) you will see that the tailtip is actually darker than the main coat, rather than lighter! 

This is the most common and typical tan pattern. There is not much to say really, you see where all markings are located. Notice the little spots on the cheeks? Sometimes they are not there, sometimes they are just tiny spots and sometimes they are big enough to become part of the muzzle markings. It varies from breed to breed and dog to dog.
As an interesting note - dogs that grow up to be saddle marked (for instance, airedale terriers, beagles etc) have regular tan markings as puppies. As they age, they go through the creeping tan stages until they are saddle marked. Other dogs stop at some point of the creeping stage and don't ever become "truly saddle-marked".

This pattern is rare in many breeds, from what I can see it is most common in hounds and mixed breeds. This type is pattern is often called creeping tan. The name pretty much explains it - the tan has a modifier that makes it creep further up than normal. Note how the tan on the muzzle and around the eyes have grown together, as have the chest markings, and the legs markings are further up. We also see a bit of tan on the underside of the dog. This pattern is fine in some breeds but in many tan-marked breeds, a dog patterned like this would never, ever place. Australian shepherds, rottweilers and dobermanns for instance shouldn't be patterned like this! I would say that when people who are a little uncertain on tan markings draw them, it often looks like this :)

This is basically just a more extreme version of the creepting tan. The head now has a so-called widow's peak marking, and we begin to see the typical harness marking behind the shoulders. 

Finally, we have a true saddle-patterned dog! Sometimes the dog will have black markings by the base of the ears (and the ears themselves can be dark too), while other dogs have completely tan heads. If you study the pictures above of tan markings, it's easy to see how the tan gradually creeps upwards. Even though there is far more tan than black on this dog, the black is still the base colour, and the dog is still genetically black with a tan marking gene! Some believe that the saddle pattern is a seperate gene from tan markings, but I don't think so, myself, and neither do many others :)
Now - for fun - imagine that this dog also had the black mask gene from the first dog... What type of colour do you get? That's right - it would be coloured like a german shepherd!

Shades

There can be many colour genes at work that affect what shades the markings can be. Of course - the base colour doesn't need to be black, either. Below I have coloured a few different dogs, that show just a few examples of what kind of combinations you can create. Of course - most breeds have very strict colouring rules. An aussie is never allowed to be black with silver markings! So it's always best to look up what colours are allowed for the breed you're going to draw :) Among the possibly base colours for tan markings, you find black, liver, red, grizzle, tan (yep - a dog can be tan with tan markings! Of course you won't really see the markings then) and many others! Below are just three examples to give an idea of the range.

Liver with tan markings

Grizzle with creeping tan and chinchilla modifier (bleaches tan)

Blue with tan saddle markings

Common mistakes

There aren't too many ways you can mess up tan markings, other than placing them in the wrong area... here's an example of what it could look like!

Woops, looks like the tan markings are messed up a bit here! I drew the tan on the tailstub to represent a tan tailtip, since this dog is bobtailed. Okay, there are a few mistakes here. If you compare with the drawings on creeping tan and so on, you realize that this dog is actually a mixture of different types of tan markings - it has creeping tan on the head, chest and belly, no tan around the vent (always incorrect), tan tailtip (never occurs in real life) and regular tan markings on the legs. Eep - this won't work! When people draw like this they normally have regular tan markings in mind so those are the ones you want to go for :)
Okay, now we have a basic idea on where and how tan markings appear! I've gone through everything I could think of. I hope you found this helpful!

Clear sable Labrador/beagle/pitbull