Kinda like the Pink eyed white and albino strands in mice that people mixed up. Though neither is trademarked. A pink eyed white mouse is very commonly called an albino but this is not true as all pink eyed white mice is PEW's are NOT albino and most don't even carry the albino gene. Albino's and PEWS actually are both separate chromosome types. Albino's will only breed true albino's as it's a ressesive trait and you can't say you have an albino unless you can prove they are strictly only (c/c) WITHOUT this they are NOT albino. PEW themselves can carry any trate which is alarming. You could breed two PEW (none c/c's) and end up with augoti's or creams, you'll never know. They are what I consider a wild card variety. However it is agreed all albino's are PEW but not all PEW are albino's...if that makes sense. Now again there are also REW Ruby Eyed Whites which are ALSO not PEW as their genotype is ru/ru showing darker red eyes with pure white fur but again NOT albino's since they are not c/c genotype. Those are some fun genetic's from a studying mouse breeder xD. We have to study their genetics to breed them.
But still I assume it's the same with mustardgas. Unless you can prove they have x for genotype as the one developed from the original breeder than you can't prove it's not a bicolored. Though even then they have the name trademarked which on a genetic level seems strange to me but...okay. I mean if you name a certain genotype something than all fish sharing that same genotype are thus that color or yours are not truly that color either but the proper name for that genotype IE is say I had a mouse with a/a/d/d/p/p and called it Starling and trademarked it doesn't make it that color, my mouse is still only a silver and breeders wouldn't take me seriously if I called it otherwise as it's not show standard. My 2 cents. But still being that mouse breeders have to study hard into mouse genetics if color doesn't make sens on a genetic level the way it's organized by show standards then it's not accepted which makes it generally impossible to trademark 'varieties' in mice. It's either approved and everyone uses it or it's a combination of two existing genotypes and considered that. (banded dutch cross, dutch piblad cross, gremlin standard cross etc.)
Edit: Bad example on the hiding augoti as it shows 100% of the time, lets go with PEW can hide chocolate, black, cream instead xD)