GRiD made black PC's before the NeXT. https://en.wikipedia.org/wiki/Grid_Systems_Corporation

There was also the Amstrad CPC: https://en.wikipedia.org/wiki/Amstrad_CPC

And the Sinclair ZX81: https://en.m.wikipedia.org/wiki/ZX81

And the Memotech MTX: https://en.m.wikipedia.org/wiki/Memotech_MTX

PDP-11's were mostly black, but I suppose that doesn't count as a "PC".