Hey all im doing a cake this weekend and its a collingwood FC cake. i have decided to colour white chocolate ganash black but im not sure what icing to use for the white.. i know obvious answer to that would be white choc ganash but i find that it has a bit of a creamy colour touch to it and im after a pure white.. one note is that i dislike the taste of fondant so i try to use it as little as possible.
any suggestions would be much appreciated!!

If your local decorating cake shop has Merckens white coating discs you could use it to make your ganache.
Although I hate to admit it Wilton's White candy discs also make a nice white ganache. You must make sure though, that the bag ssays white on it because there are two kinds the one with the slight ivory color and the pure white ones.
Hope this makes sense.

I think the Merckens one is called Super White.

Either add white food coloring to your Ganache or make BC with Crisco that will give you a very nice "white" icing
HTH

You must be a fellow Aussie then? If so, then you probably won't be able to get Merckens discs, and possibly not the Wilton white candy discs either. I would second the buttercream made with vegetable shortening suggestion. Any buttercream made with butter is going to be off-white at best. You could of course use royal icing, but let's face it - nobody is going to want to eat that. The other option would be a marshmallow frosting, which is like IMBC without the butter.

For the black you said you were planning to colour white ganache black, ...have you considered using dark chocolate ganache to colour black? - you would use much less colouring that way. Also you may need to use an oil-based food colouring if you plan to be adding a lot of it to ganache.

Personally I'd stick to using the one icing type for the whole cake. I would figure out what I had to use to get white, and then use that for the black too.

does using shortening to make BC give it a different taste?

BC with shortning is the only BC i make, like Coral said add whatever flavour you want, I personly add a lot of vanilla