Australia-based packaging firm Caps & Closures has developed ThermoShield, which are customizable color-shifting caps. "Thermochromic materials change their colour with temperature change," the company writes. "This technology promises to play a massive part in any packaging where product quality is dependent on temperature."
Customers can specify precisely what temperature they want to trigger the color change, and whether they want the change to be permanent (i.e. "These goods are spoiled forever") or reversible (i.e. "These goods have reverted to safe-to-use.") And the color-changing ability "doesn't wear out in normal use," the company says.