
I agree with LucyDogs. I know of several well respected Show kennels who breed parti to wholecolour litters. I have done it myself and as a fan of widening the gene pool (on the basis of HEALTH) I disagree totally that it is a bad thing. I think it is on this basis that more good breeders are now willing to consider parti to wholecolour matings. So long as you know your pedigrees then you can minimise the risk of bad mismarks. A little bit of white on a chin is nothing serious at all (purely cosmetic) and I think if the pup in question is good quality then it could be shown quite successfully. Some judges will penalise for it of course.
My B&T bitch pup has a tricolour Mum (her grandmother was ruby) and a ruby sire (from a strong wholecolour line). All 6 pups in the litter were B&T as I anticipated, with just minimal flecks of white. I would not consider mating this little bitch to a particolour though as that would produce mismarks. I will find a quality dog from a wholecolour line for her when the time is right.
I also bought in a ruby last year - blenheim Mum ruby sire. Both parents from top quality lines. She has a tiny white mark on her chin, you only have to glance at her to see she is from sound quality breeding and the bit of white really is insignificant.
I think it would be silly to write a pup off just for a bit of white on chin and chest. The white will diminish over time anyway.