Old English sweart "black, dark," of night, clouds, also figurative, "wicked, infamous," from Proto-Germanic *swarta- (source also of Old Frisian, Old Saxon, and Middle Dutch swart, Dutch zwart, Old Norse svartr, German schwarz, Gothic swarts "dark-colored, black"), from PIE root *swordo- "dirty, dark, black" (source of sordid). The true Germanic word, surviving in the Continental languages but displaced in English by black. Of skin color of persons from late 14c. Related: Swartest.
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy).
also schvartzer, "black person" (somewhat derogatory), 1961, Yiddish, from schvarts "black" (see swarthy). Perhaps originally a code word to refer to black servants when they were within earshot, as German cognate Schwarze appears to have been used mid-19c.:
In Baltimore in the 80s of the last century, the German-speaking householders, when they had occasion to speak of Negro servants in their presence, called them die Blaue (blues). In the 70s die Schwartze (blacks) had been used, but it was believed that the Negroes had fathomed it. [H.L. Mencken, "The American Language," Supplement I, 1945]