The Jewish Holiday
This change was made for those who observe Passover. Many foods are forbidden during the Jewish holiday, and corn syrup is one of them. However, sucrose is okay to have, so Passover-observant drinkers can still enjoy Coke; they just have to make sure it has the yellow cap!
Kosher
These special caps tell people that it’s a kosher beverage for Passover. In a sense, it’s a stamp of approval. During Passover, people can’t eat or drink things that aren’t kosher for Passover, which involve traces of wheat products. It happens during one spring week a year, and various customs must be observed.