I have read in my grammar book that after colour adjectives we can often leave out one/ones in answers. But what about questions? Are all following questions good?
Which car is yours? This blue, or that red?
Which car is yours? This blue one, or that red?
Which car is yours? This blue one, or that red one?
Best Answer
I'm struggling to fault these from a grammatical standpoint, yet they don't sound natural to me as a native British English speaker. I think the reason they sound weird is that you are using 'this/that' to differentiate between the cars but also bringing their colour into it. When we use 'this' and 'that' it should be clear what or who we mean. For example, we might point to something nearby and say "this one?" or point to something in the near distance and say "that one?". If we used that method to identify a car, the colour would be irrelevant.
If faced with distinguishing between just two vehicles of different colours, we could ask, without any need to point, "is your car the red, or the blue?". It would be equally common to ask "the red one or the blue one?"
Alternatively, if faced with distinguishing between two vehicles of the same colour, it would be necessary to identify which car you were referring to in some other way, such as pointing or gesturing at them. For example, you might ask "this red one, or that one?", as you point to each in turn.
I can't imagine a situation where any of your examples would be used, or at least lead to a satisfactory answer. Imagine a scenario where you had been told your friend owned a red car, but you saw two red cars. If you pointed to one of the red cars and asked "is it that red one?" because you genuinely did not know which car belonged to them, you'd surely just be pointing to a random car and guessing? You would surely just ask "which red one?". If you did want to take a guess, the colour would still be irrelevant because that has been established.