Welcome to YT!
Yes it is rare to have a solid colored yorkie,but it is not allways a good thing. From what I've read here on yorkie talk,the all blue ones are suseptable to having more health issues. I'm not sure about the chocolates. You could click on the searsh button and mabie type in (solid colored yorkies) and look thru some of the old threads about them and find out alot more than what I can tell ya. I deffinatly would not pay extra for one if a breeder was to ask more for it, just becouse I dont believe they fit the standard as far as the coloring goes. Sometimes breeders will call them rare to get more money,just like calling the runt of the litter (teacup) for more money. Hope this helps.