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I don't know what percentage of yorkies shown in the US are dyed but do know many are "enhanced" with hair dye. In fact, some of the well known show breeders and handlers secretly take pride in their "dye" colors.
Also, I don't know specifically about Norway but am aware many European yorkie show breeders practice dying yorkie coats. So, it is not a "cheat" exclusive to the US at all.
My opinion? I really don't care as long as everyone gets to dye their dogs. I don't understand how the truth can be so well known amongst show people, and accepted within the show community even though it is a disqualification? Where are the "ethics", we are told are so important to look for in a show breeder when the entire yorkie show community condones this?