If just one color is out, have you thought about the possibility of a bent pin? Sometimes when connecting up a VGA plug, not all the pins fit neatly into their respective sockets. The result is a bent pin that gets pushed down into the bottom of the plug. Depending on the pin, you can have varying results. Depending on the pin, that could mean the loss of certain colors. Check it out! (Hope I didn't post here too late if that really is the problem.)