Inexpensive plastic developed that indicates freshness of food

Inexpensive plastic developed that indicates freshness of food: "When it comes to buying packaged meat and fish, consumers usually just have to go by the 'best before' label to know that it hasn't begun to spoil. Needless to say, the dates on those labels are just estimates and certainly won't tell you if the product has sat through a lengthy power failure, or been left out of the cooler for several hours."