"The error light on the Epson Stylus color IIs keeps blinking. The color cartridge is new. The black and white prints perfect."
(From: Robert J. Brancatelli (bronco@mkol2.dseg.ti.com).)
Most likely, the new color cartridge is not seating all the way. Move the print head to where you normally do to swap the heads. Now, without removing the color print head, lift the most forward lever up as far as it will go, then bring it down to reseat the ink cartridge.