Depends on how you want to dim the color of the characters. A transparent layer of some sort that’s a super light blue above all of them? XD

It comes down to the overlay layer and the lighting effects of the background. Study photographs of underwater scenes and try to recreate the light refraction in them. The effects you've used here work for a surface of the water, but not so well for beneath the water. You would see more light rays and diffused light than shimmers of waves.