You should know that you shouldn't ever give a dog, or any animal for that matter, chocolate. I don't know what could happen but I know I wouldn't give it to my dog!
It seems that white chocolate would be safer since it is the theobromine that is bad for a dog, and the darker the chocolate, the more theobromine it has. However, white chocolate is mostly cocoa butter and sugar. It might have a small amount of theobromine in it, and it is quite fattening. Sometimes, white chocolate doesn't even contain cocoa butter, but is essentially confectioner's glaze (fat/grease/margarine and sugar).