Английский Этимологический словарь - yell (v.)

YELLOW - O.E. geolu, geolwe, from P.Gmc. *gelwaz, from PIE *ghel-/*ghol- "yellow, green." Adj. meaning "light-skinned" (of blacks) first recorded 1808. Sense of "cowardly" is 1856, of unknown origin; the color was traditionally associated rather with treachery. Yellow-bellied is from 1924, probably a rhyming reduplication of yellow. Slang yellow dog "contemptible person" first recorded 1881. Yellow journalism "sensational chauvinism" is 1898, Amer.Eng. from newspaper agitation for war with Spain, originally from use of colored ink in "Yellow Kid" comic strip as a publicity stunt (1895) by the "New York World."