Egg Tag / Freshness Indicator

How to tell an egg is fresh or not is a tough question in daily life. Although there are some small tricks, for example, submerge the egg into the water or simply check the production date to refer to the freshness, they are not convenient at all. Inspired by chemical indicator, the pH of solutions can be expressed in different color scale, what if the freshness of the egg can be expressed in different colors as well? Since during the oxidation of egg, it will constantly release carbon dioxide and its amount can be set as the variable to determine the freshness of the egg.