
Regardless of how yellow occurs in the breed the point I was making is that it is usual to endorse the pedigrees of the yellow flatcoats, as we would discourage breeding for a supposedly rare colour. We all know as soon as something is described as rare there will always be people out there who want to make a fast buck and do not care how they do it!
The OP tells us her friend is very sensible, which is good, so would understand if the pedigree was endorsed why. If the pedigree is not endorsed so that you can compete there is nothing to stop you entering a yellow in a show or any other competitive event licensed by the Kennel Club. However it would not be right to mis lead people by saying that these dogs can be shown, with success. The link You mention does say third at open show but that is in Scandinavia. You cetainly would not get placed in the UK at a show. I would not sell a yellow with out the pedigree being endorsed progeny not suitable for registration.