What is comparative form of red?

The comparative form of "red" depends on what you're comparing it to:

* If comparing red to other colors: You would use redder. For example, "This apple is redder than that one."

* If comparing the intensity of red: You would use more red. For example, "This shade of red is more red than that one."

Note: While "redder" is more common, "more red" is also grammatically correct.