Excellent web site on coat colors! In very short terms, I was told that "merle" hair is a multiple color on each hair, creating the merled coat. With the blue ACD such as seen in the picture above, EACH hair is one color, but they are intermixed throughout the body. Ingrid, would you agree? That doesn't answer the original question, as I do not know about DQ in showing purebreds, I just like the article (and the science behind it)

Papillons are a marked breed like the berner or dal. In their case although it's historically inaccurate it is used as the identifier of the breed vs. other similar looking dogs like the LH chihuahua or pom. Historically papillons were the drop ear variety called phalenes and any color or color combination. According to the 1935 standard in akc any color or color combo was allowed then somewhere between 35' and 75' the standard changed.

Color pretty rarely comes up in this country because such a wide range of colors is tolerated so long as the leather is black, but other registries overseas do allow livers and I know of one blue born in this country to a litter of black and whites with black and white parents.

Again, I wish I knew the whys on the intolerance of liver shades but my suspicion has to do with a time period where liver was not thought highly of among breeders in other breeds.

The blue and isabella dobes are accepted in US but not in Europe and the reasoning behind that is quite obvious- the dilutes usually have skin problems and thin hair (to the point of bald areas). My friend has one, takes really good care of her with feeding and lotions and stuff. According to a trainer that occasionally trains in US and has seen blues there, her dog is gorgeous with really good hair and skin but unfortunately doesn´t even compare to a normal black or brown. A high-maintence dog like this really can´t be all that practical as a service dog that dobe is supposed to be.

In dachshunds the double-dapple is not allowed anywhere and again this is pretty obvious as there are several health issues that they often suffer. HERE is a short article about it with a few pictures.

I know this is getting to be an older thread, but to answer your question about merles, Katie, breeding red merles is looked down on in many breeds, not because they aren't pretty (I've seen a few that are absolutely gorgeous), but because it's sometimes difficult, especially in adults, to tell a red merle from a normal non-merle dog. Apparently it's often pretty easy to tell when they are puppies, but the markings tend to either fade or blend as the dog matures.
I actually had a sandy-brown mixed breed dog with a small black saddle on her back. If she hadn't had a ragged, patchy pattern on the saddle, I would never have suspected she was merle, just really poorly pigmented, even though her ear tips did have some faint mottling.

Dogs with only one merle gene are usually fine, but those with two (homozygous) often have serious issues like deafness and tiny or missing eyes. The idea is a red-merle dog might be unknowingly bred to another merle and produce homozygous merles. Some breeders produce homozygous merles on purpose because the offspring of homozygous merles will always be merle which is a selling point to some people. All in all it I think it makes more sense than most other color restrictions.