"A Dudley Lab is a Labrador retriever that lacks pigmentation on the eyes, eye rims, muzzle, and nose.
This is a genetic trait that is very rare and affects only the yellow Labrador retrievers.
This trait can't be considered as an abnormality of the genes.
Usually yellow Labs have black pigmentation on those areas while Dudley Labs don't"
A yellow lab may have a light nose, snow nose, and not be a dudley. Dudley refers to the lack of pigmentation of more than just the nose, including the gum tissue and eye rims. If it does not lack pigmentation, the dog is not dudley.
Here is a good page
Better article with pic