Animate colour change along object to simulate direction of flow

Hey everyone,

I'm trying to produce an animation involving a group of pipes (not hollow) where the direction of flow is indicated by a bright colour moving along the pipe in the relevant direction. However, i'm not sure how to achieve a nice smooth 'flow' of colour.

I've tried animating the materials, however can only get the whole object to change colour at the same time. A 2D example of the kind of effect i'm trying to achieve is in this flash game when you click on the tap to start the water flowing and the white is gradually replaced by blue - http://www.addictinggames.com/puzzle-games/plumber1.jsp.

Any advice of where to start or areas to explore would be greatly appreciated. :)