black it is. means black.

It means "let's decide on black" or "let's choose black" :)

"Black it is!", is an informal way of saying, "Sure, we'll get blank." It's just another way to confirm an agreement to the choice .

The idea is that you might debate several options with someone, and when you are done, you add ‘it is’ to indicate it is the final choice that you’ve agreed on after a discussion. Where do you want to go on vacation? Long discussion about the pros and cons of different places. ‘OK, Spain it is.’ (Spain is what we agree is best after a discussion) Here, it seems to be a joke because Howard is just making the decision by himself. Adding ‘it is’ communicates that he’s not interested in what Sheldon thinks.

No, “black it is” and “is it black” are not the same. “Black it is “ is the final decision ,so he is saying he is going to pick black then. “Is it black” is a question.