Make sure the 2 other places where the color comes out of the ink cartridge are open. sometimes there is a sticker or something over them to keep them from leaking, its possible that only the red side is open.
if it is a tri color cart it may be defective. trade it out and see if it still does the same thing. if it does, you may need to clean the printer and see if you have any built up ink sitting where the cart heads rest.
if the cart is not defective and is in fact a tri color, i'd get in touch with HP and fill them in on what's up. there may be some settings that need to be adjusted.
hope this helps.