The red colour of Jelly is due to addition of

The red colour of Jelly is due to the addition of Charring of sugar.
When sugar is continuously heated in a dish, then it starts evaporating and becomes foggy due to water vapour. A black powdery substance is left behind, which is charcoal. This process is called the charring of sugar. It is an irreversible chemical reaction.
This charcoal colour adds red colour to the jelly.