One approach to finding slang words in texts, or other potential clues to identify BAME presence, is to spell check the document and review the unknown words. This is arguably a benefit of working with modern tools, which are generally trained on modern, especially, born-digital, texts. Older terms, which are relevant to us, may well be unknown to spell checkers trained on modern materials.
Using MS Word as an example, we see that our list of descriptive words produces four errors (bold words):
negro, negress, mulatto, quadroon, quarteroon, fustee, mustee, dusky, nabob, anglo-indian, swarthy, blackamoor, moor, african, torrid zone.
The first two errors are spelling issues, the latter two, capitalisation. This suggests that the approach might be worth further consideration, though it will depend on the quality of digitisation. Some historical source materials are simply scanned and OCRed, without further curation of the automatically generated text. The first two steps are relatively quick, cheap and easy; the latter one, slow, expensive and hard. However, without this curation, the resulting text can be of poor quality, especially when dealing with historical texts that not only have the problem of working with ageing documents, but contain words that the OCR engine cannot recognise because they are not in its modern-trained spell checker!