Could Latin niger "black", of uncertain origin, come from *negʷ- "bare, naked"?
For an analogy, compare black, blank, Spanish blanco "white, argent", and their roots PGem *blakaz "burnt", PGem *blankaz "white, bright, blinding", PIE *bʰleg- and *bʰleyǵ- respectively, both “to shine”. bleak in OE could mean "shiny", from PGem *blaikaz "pale, white", also from PIE *bʰleyǵ-. All taken from wiktionary, none sourced but often taken from LIV or Pokorny.
At least bleak and niger both have negative connotations.
Ger. Blanker is short for blanker Hintern "naked butt"; blankes Kabel is an exposed, unisolated wire, perhaps not dull (oxidized) so as to be conductive.
Supposing there was the slur *nig- or *neg- "slave, dark skin" (cp. nigger, negro, Neger) or something close, which should be hard to falsify, the idea is it would have been formative for niger, because one common justification for enslavement, not just "Negroes", was incivility, and that would stereotypically include nakedness. Also, slaves would have to appear naked at auctions and often cater to sexual submission.
For comparison maurus "Moor, Mauritanian, African" is comparable to Ancient Greek μαυρός (mauros) "dark, black, dim, weak, ...", which is uncertain but might derive from the name of the Moors. (Edit: notes of unyielding comparisons removed)
I'm afraid I'm too pessimistic, and downright paranoid about not being pessimistic enough about the darker parts of history. So, any input would be appreciated, in comments. Although, an answer should focus on publications on the matter.
Following maurus, I wonder, can a comparison Nubian versus nudus "nude" be fruitful? nudus is derived from PIE *nogʷedós through *gʷ > Lt. u (thanks @TKR), but b < du is not unknown in Latin (cp. bellum, duellum). The etymology of Nubia is unclear to me, not Egyptian apparently, unless from nwb "gold".
A term encountered in Roman ideas about slavery is social death. Hence including necro in the comparison might be helpful. The negation marker *ne should be considerable. Insofar the actually used word was mortis, mors, cp. maurus.