Sure it is, or at least in my English (which I have been speaking my entire life) :) "What's the color of the house?" "The color of the house is red." It may not be the most common way of saying this, but it doesn't make it unidiomatic or ungrammatical.
This questions exists to teach you the consonant mutation in "renk."
Well, we'll just have to agree to disagree then. If you told me "The color of the house is red," I would assume you weren't a native English speaker, or at least think it was an odd way to get your point across. I know that the question serves a useful purpose in terms of Turkish, but they could easily find an example that translates better to English, or just allow "The house is red" as an idiomatic translation.