Something like this?
http://www.raamw3rk.net/projects/uitburo/index.php
As Mark said, Generate > Fill will render the layer a single color.
You can play with shades of colors to suggest depth.
Depending on the look you're creating with water filling up the titles, you could either just animate the water surface or indeed shoot something in a small tank. You'll need to make sure the water is 'wild' enough otherwise it will just end up looking like a slightly animated mask - in which case that would be easier to do.
As for shooting the fluid: milk in front of a black background will be easier to get a nice matte from.
Bar3nd
Raamw3rk - digital storytelling and visual effects
