Black & white picture through an HDMI cable?

Hi all, I bought a Samsung LE40R88BDX/XEU almost 3 years ago now and its been a smashing tele until this week when suddenly the picture went black & white. It is connected to a sky+ HD box with an HDMI cable, I changed the cable but no change. I hooked up the sky box with a scart lead and got a colour picture. I hooked the sky box to another tele via HDMI cable and got a colour picture so obviously it is the HDMI connections on the TV that is at fault. I rang a TV engineer but he said that he had never heard of this fault and was unsure how to fix it.
So can anyone out there tell me if it is fixable and approximately how much it would cost to put right. Many thanks