If a white person takes what a person of colour says seriously, it does not imply that the white person does not question the claims of the person of colour. If a white person takes what a person of colour says seriously, it means that the white person does not dismiss the claims of the person of colour. “Dismissing” includes the white person considering what a person of colour has said and then rejecting it because he has never experienced it himself and has never heard of such a thing before, and then reconsidering it later only because enough people of colour started telling him the same thing.
That you have never experienced something yourself is not a valid reason to reject another person’s experience. If you are white and a person of colour mentions something that you have never experienced before, it does not mean that the person of colour must be lying or hallucinating. It could mean that you are not omniscient, and not more knowledgeable about everything than any person of colour. Given these two possibilities—either you are (i) not omniscient and not more knowledgeable about everything than any person of colour, or (ii) the person of colour must be lying or hallucinating—there is a higher probability that you are ignorant about something, and the person of colour is telling the truth and not suffering from hallucinations.