Why is it that black people n brown people look dirter even if they are very clean actually and white people look clean always?

i am a brown man n i get this feeling when i look at people of different colour.
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+1 y
could it be because when everyday objects get dirtier, they first become brownish and then blackish?
Why is it that black people n brown people look dirter even if they are very clean actually and white people look clean always?
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