hi，usually we dont say 黑美国人，we just say 美国黑人.if you say 黑美国人 we will think like that——oh, maybe you mean an American whose skin is black .or , you know in Chinese , when 黑 is used as a verb, the word 黑 also means that A spread some bad and exaggerated words which is about a collective or a famous person B on purpose.