In a bowl over gently boiling water put in white chocolate and butter slowly melt (make sure the bottom of the bowl doesn't touch the water) let it cool slightly.

Put egg whites into another bowl and whisk until light and fluffy and stiff enough to hold a peak when u remove the whisk

In another bowl mix the egg yolks and sugar together, then add in the cooled white chocolate and butter, mix well

Gently fold in the egg whites into the chocolate mixture, keeping in as much air as u can to keep it light and smooth

Separate the completed mousse into three equal amounts, keep one white. Then in the next bowl add enough red food colouring to get a deep flag red, also do the same in another bowl with the blue food colouring.

To assemble get some nice glasses and put In a layer of red mousse, allow to chill in the fridge for fifteen to twenty minutes (also store the other two coloured mousse in the fridge - this helps set the mousse quickly), then add white mousse on top of the red. Allow again to chill for fifteen to twenty minutes. Finally add the blue layer and leave in the fridge until it's time to serve (this can be made a day in advance)