"Is this your new, black coat?"
Translation:C'est ton nouveau manteau noir ?
1st sentence: "est-ce que" is an expression to introduce a question. It means "is it that", then you need to build the question itself with a verb.
2nd sentence: the verb is the first word of the sentence: est = is, then ce = it. It is exactly like the English "is it", like "is he" (est-il) or "is she" (est-elle)...
The question asked is not to know whether your new coat is black or red, as suggested by your proposal.
In English, "est-ce que ton nouveau manteau est noir ?" would be: Is your new coat black ?
So it does not work.
So let's start again from the beginning...
If you are given the English sentence first: "Is this your new, black coat?", you have 3 options to translate it in French, from formal to standard to casual:
-> Est-ce (= is this) ton nouveau manteau noir ?" (adjective placement: subjective first "nouveau", objective second, and after the noun)
--Note: formal questions with a pronoun (il, elle, on, but also "ce") use an inversion Verb-Subject
Variants in French, with the same exact meaning:
-> est-ce que (consider that as a block) c'est ton nouveau manteau noir ? (standard French, less formal, no inversion, use of the question block "est-ce que")
-> c'est ton nouveau manteau noir ? (informal, oral French, no question "block", word placement similar to an assertive sentence)
--Note: to make it a question, in writing you add the question mark (?) at the end and in oral, you raise your voice at the end of the sentence.
If you refer to the following link, you will notice that 95% of adjectives are placed after the noun, in French. When you have 2 or more adjectives, they will be placed according to their degree of subjectivity (your judgment on the object) vs objectivity (reality).
- un manteau noir (general rule "95%")
- un beau (subjective) manteau noir
- un grand (rule "5%") et beau manteau noir.