You could pretty easily do this with the Noise plugin - to duplicate the example you've shown, you'd need to make a 3D layer, and align it to the camera so that it's above, almost like a sky, which of course, the surface
would be from underwater.
Play with the noise settings, and maybe add a Threshold effect to cut down on the number of "reflections" moving around. You could add a Tritone effect to get your colors, or a Colorama effect could give you a wider range of colors. If you want your "hero" to look as if he's underwater, you could add a distortion map which uses the water layer to distort him, the way water refracts. You might also use a Compound Blur, using the water layer, to blur the hero to match. Depends on the level of reality you want, given that it's a cartoon.
Joe Bourke
Owner/Creative Director
Bourke Media
http://www.bourkemedia.com