hope is a good thing but it doesn't replace logic.
first off, before lugging the TV back, I'd try another source, say a DVD player that upscales/upconverts to HDMI. don't expect a HDTV quality picture but it should be at least very good and the colors should be correct.
With this you can verify that the TV's HDMI inputs are either working correctly or faulty. If you choose, you should be able to return the DVD player, assuming you abide by the store's rules.
Second, is this cable HDMI at one end and DVI at the other? interesting...