Black is black all over, and the feathers are dark all the way down the shaft. Here's my black rooster:
The fluffy butt behind him is a blue. Blues can vary wildly, from so light they can be confused with splash to so dark they can be confused with black. Here are some of mine:
^ These are all blues, yes even the Sizzle. If you are unsure of whether a bird is black or blue, breed it to splash. If the bird is black, all of the chicks will be blue-if its blue you'll get splash and blue chicks. If you breed your unknown blue/black to blue, all chicks will be blue or black. Either way, black doesn't make splash. So, if you're getting splash chicks, someone is not black
The fluffy butt behind him is a blue. Blues can vary wildly, from so light they can be confused with splash to so dark they can be confused with black. Here are some of mine:
^ These are all blues, yes even the Sizzle. If you are unsure of whether a bird is black or blue, breed it to splash. If the bird is black, all of the chicks will be blue-if its blue you'll get splash and blue chicks. If you breed your unknown blue/black to blue, all chicks will be blue or black. Either way, black doesn't make splash. So, if you're getting splash chicks, someone is not black
It doesn't really matter, they are great. Just haven't hatched one so light yet. 
What color do you think the lightest one will feather out? We've never hatched one so light from two blue/black parents. Just a lighter blue? 