red cent (n.)
type of copper penny, 1839, American English, from red (adj.1) + cent. Pure copper pennies were issued 1793–1857, then replaced by ones of copper-nickel and, after 1864, bronze. The old cents were disused, but the phrase remained colloquial as a mere emphatic of cent, usually in the negative (don't have a ... not worth a ...). "Red" has been the color of copper, brass, and gold since ancient times.