The short and simple explanation is to copy the path of the shape layer, paste the path to a new layer as a mask, apply stroke to that layer animate the stroke, use the animated stroke Mayer as a track matte for the shape layer then duplicate the pair offset the timing and. Hangs the color of the second shape layer.
Thanks for that rick... I actually have that part already set up and working... Although it was done so slightly differently from your method, which gives me a different insight as to another work around, so thanks. But my real query is to whether I can apply a gradient to this top coloured layer so its tail end is faded to white, is this possible?
There are gradient stroke options in Illustrator that are not available in After Effects.
This gives you something like this in After Effects and you can use Gradient Wipe to reveal the path.
You could then use the animation as a track matte for another layer. There are a host of possibilities. Here's a project file for you to look at. I hope it gives you some ideas.