Similar to the thermochromatic cans and labels on beer commercial, these caps will turn blue when the beer is cold. They are light a gray when warm (see pictures).
They also have a plastic liner containing an oxygen absorbing agent, that absorbs oxygen from the head space. These caps are necessary for long term storage of beer (over one year).
5 gallons of beer in 12 oz bottles uses 53 bottle caps; 5 gallons in 22 oz bottles uses 29 bottle caps.