Item in Main Hand / Off Hand, Right Click Block : Color in the Applicator will be Applied to the block.

Item in Main Hand / Off Hand while Crouching, Right Click In Air : Cycles Through all Colors in Applicator

Item in Main Hand / Off Hand while Crouching, Right Click on Colorable Block : Copies the color of the block to the Applicator if it doesnt already exist (will override the first added color if the applicator is already full of colors). If the color already exists, it will swap to that color in the applicator selection instead.