It has to be something else. I'm not saying you don't know this, but to be clear, HDMI is the smaller cable.
Look at this site, we aren't playing you, it is the best, and it has a picture of what it looks like: CNET Quick Guide: HDMI and HDMI cables: What is HDMI? - CNET Reviews
You bought your cards brand new? Perhaps it IS 3 bad cables, where did they come from? Your monitor supports Windows 7 and HDMI?
Failing all that, perhaps you just need to edit your display's settings. Edit the monitor settings itself to see if you can clear it up, edit the control panel settings dealing with your graphics card (Mine is Nvidia Control Panel, for example) to optimal levels, and double check color and display settings in windows control panel.
*EDIT* You know, perhaps it is the monitor just not working with the HDMI. Buy a new one and it may solve your problems. If you don't want to upgrade that, test someone you know who has an HDMI monitor and see if it is indeed your monitor