The ganache frosting I use comes from a book called 'Planet Cake' by a cake decorator called Paris Cutler, Australia.
Her recipe is:
600 ml of pure cream to 1.2 kg of cooking chocolate
1. Boil cream over a double boiler until it just reaches boiling point
2. Remove from heat, pour in chocolate and stir until completely melted
3. You may put it back on the heat to melt the chocolate
4. Let the chocolate sit and cool until it comes to a spreadable consistency - its spreads, but isn't runny and doesn't drip
-a big tip: make sure you use PURE cream, nothing that is thickened or already whipped, otherwise the ganache wont work. The one I use has a 45% fat content.
As an idea, this will make enough to cover a 14" square cake that is roughly 6cm high, with ganache in between the cake sheets, plus some! It makes quite a lot.
I covered cakes in a dark chocolate ganache, and then a layer of white fondant and no colour showed through, it was fine. You don't need to make it overly thick, just your standard thickness.
Hope that helps and good luck!