Here's an example of a little packaging gimmick that Japan's Morinaga is using to spur interest in its Dars chocolate brand.
To differentiate itself from competitors, Dars claims to offer "high quality mouth meltiness." According to Morinaga, the chocolate is best enjoyed at 22 degrees Celcius, and to assure that consumers know what temperature the product is at all times, the company invented temperature-sensitive stickers to affix to Dars packages.
At around 22 degrees the label dot is a deep pink. Below 19 degrees it reads purple, and above 25 degrees it appears light pink.
While the majority of customers are probably not paying much attention, the addition of this new bit of technology creates a PR opportunity along with a reason to buy, especially amongst teens and kids who'll likely use the package as a conversation starter or as a toy.
Additionally, Morinaga has leveraged the idea of optimal temperature consumption in a consumer promotion involving a prize drawing. 
To enter, purchasers must collect 5 proof of purchase marks and send them in along with their contact information. 800 winners will be randomly drawn from the entries and receive their very own "chocolate cellar" that purports to keep Dars chocolate bars at an even 22 degrees.
