You change the colour of shields in the player .entity file. But you also need to increase their visibility... there's a nifty tutorial I posted a while ago on how to do that, just search around this forum.
As for the shields themselves, they are also a mesh. This means you have to create a bigger shield model in your favourite 3D modelling package and import it into Sins. If you want shields which follow the outline of your ship, you will have to use a low poly version of the ship model and resize/edit it so that it fits the general shape of the ship. Afraid there's no easy way around it unfortunately.