MILK CARTON THAT CHANGES COLOUR TO INDICATE FRESHNESS

I am one person who would buy a carton of soya bean or milk, drink a bit and leave it in the refrigerator for some time.  Very often, I find that the soya bean or milk gets spoilt when I next want to drink it.  Do you have a similar experience?
Recently, I discovered that someone has invented a milk carton that changes colour before expiring.
Here is the write-up

MILK CARTON THAT CHANGES COLOUR BEFORE EXPIRING
What a great idea designer Ko Yang has had with this milk carton that changes color telling us how fresh the milk is. The carton begins being white in color, and as the expiry date moves closer, it begins changing color to tell us we should drink the milk before it’s too late.
A brilliant way to help us consume our food without wasting any, something to which other ideators have already given some thought:
(31999) Expiry date for products that have been opened
(2255) Visual warning for expiry of food products

Source: http://blog.ideas4all.com/blog/2010/04/01/the-milk-carton-that-changes-color-before-expiring/