Why oh Why do supermarkets sell stuff in black plastic trays?

Please tell me why supermarkets are selling stuff in black plastic trays? We cannot recycle them in Shropshire - even the most modern. sophisticated plastics separation facility can't do anything with black trays!! So why is stuff still sold in them? Are the black trays cheaper to produce? Does the food look better on a black tray? Either way, there should be a way that forces non-recyclable packaging out of the loop. Perhaps, there should be a disposal surcharge on products if their packaging is non-recyclable to discourage food companies from using it. Perhaps, supermarkets could start to refuse to sell products which come in non-recyclable packaging.... Another idea would be for supermarkets to provide the facility to take back all their own packaging.... all the bring banks in the car park are a good start - but if supermarkets had to find recycling and disposal routes for all the packaging they sold - they would soon start to only sell things wrapped in stuff that is easy and cheap to handle. Oh for a joined up World...