Our Standard has included basically the same color requirements and disqualifications since they were added in 1911. During the intervening 97 years, it has listed the following as disqualifications: solid black, black and white, black and tan, liver and mouse color. In the FCI (Fédération Cynologique Internationale) Standard, the term "mouse grey" is used (Mausgrau in German, gris souris in French). Since our color disqualifications were added the same year that a Conference of French Bull Dog Clubs of Europe, at which our club participated, developed the European countries' standard, it is clear that the "mouse" in the US Standard referred to the mouse-grey coat color shown by dogs expressing the recessive "blue dilution" (D/d) gene.
which may range from reddish through yellow to pale cream; and a dark pigment (eumelanin) which is either black or brown. French bulldogs should carry only the gene for the black type of dark pigment and therefore should have only black noses, lips and paw pads.
Brown pigment in the coat or nose/lips/pads is unacceptable (and is the "liver" that our Standard deems a disqualification; it is also a DQ by the FCI standard). The light pigment gives rise to a range of fawn coat colors all phaeomelanin, but in various degrees of concentration to produce the range of pigmentation from red through fawn to cream. Some fawn Frenchies have a black mask, which is a recognized and acceptable coat.
French Bulldog another 'pattern" gene produces pied (piebald) in which the coat is white with pigmented patches most commonly located on the head, tail base, and "saddle". The pigmented patches may be either fawn or brindle, but in a brindle pied dog there must be enough fawn hairs visible in at least one of the pigmented patches to provide the brindle pattern, so that it is not the disqualified "white with black."
Another pattern gene gives rise to black-and-tan (black with tan points), also a disqualification in both the US and the FCI standard. While there have been some black and tan Frenchies, these are rarely seen.