What part of the electromagnetic spectrum is most absorbed by water?

Water is cyan because it absorbs red light. The froth in the waves is white because, like clouds, it is composed of variety of tiny water droplets that scatter light of all the visible frequencies.

Water is transparent to light of nearly all the visible frequencies, it strongly absorbs infrared waves. Water molecules resonate to the frequencies of infrared. Energy of the infrared waves is transformed into internal energy in the water, which causes red light to be a little more strongly absorbed in water than blue light.

Electromagnetic waves that stimulate the sensation of color when the vibrations interact with the cone-shaped receiving antennae in the retinas of our eyes. Our eye-to brain interactions produce the beautiful colors we see.