If someone points to a wall and asks, "Is this wall really yellow?", a proper answer to such a question would be something like "No, it's not really yellow. Just take off your sunglasses and you'll see" or "Of course, what would you call this color if not yellow?".
The person, however, may be using the exact same words to ask a totally different question, a question to which the above answers would not be acceptable. Suppose you answer, "No, nothing is really yellow, for colors are subjective." He may disagree with you or ask you to clarify what you mean by "subjective", but at least you are giving him the right kind of answer, namely, a philosophical view of the thing in question.
Indeed, if the light is normal, the person is not wearing a pair of sunglasses, the wall is clearly yellow, etc., the question "Is this wall really yellow?" would not make any sense except as a philosophical question. But what does it take for a person to ask such a philosophical question?