One description of a tricolor is the color of a Rottweiler or a black Dobermann with the addition of white markings. Can Ch Banchory High Born ROM is the top producing tricolor in breed history. Not all black dogs have the tan points. At one time the lack of tan was considered a fault, but in fact black or black and white without tan was an original color of the Sheltie, and it is now once again fully accepted. The Piano Man ROM is an outstanding example of this color, which is often called a bi-black.
Blue merle is the result of a diluting gene, called merle, on a basically black coat.
If the dog has the genes to be a tricolor, it will be a blue merle, tan and white, often called just blue merle. The coat dilution is rather splotchy, so a blue merle will have the parts of the coat that would otherwise be black diluted to blue-gray with varying splotches of black. This is probably the most variable color in Shelties, with the blue part of the coat varying from a clear silver blue to a pewter color, and the amount of black varying from flecking or marbling of the coat to patches that cover most of the body. The tan points do not show obvious merling unless a masking factor produces black tips. The merle gene can also affect how much area white markings cover.