Cookiebaker, here is a website that may answer some of your questions.
www.justlabradors.com
Someone had posted this link on pettalk before and I saved it. Look up the breed standards and it tells something about blacks, yellows and chocolates and what is standard. Like some blacks can have a spot of white on their chest and its ok. I think it was somewhere on this link that I read about the genetics of yellow and yellow breeding only gets yellow but if mixed with black you get both black and yellow etc. You should have some fun at this website!
I am sure you will love their photo gallery! I do!