Please note an Australian cup is based on a 250ml cup.
Food colouring for the cake layers: AmeriColor works really well to get the intense colours. I used colours: 106 Electric Blue, 107 Lemon Yellow, 119 Red Red. If buying small bottles I would recommend buying a larger bottle of the red as you will use the most of this colour.
Cake colour mixes: Red layer: just pure red. Orange layer: Yellow and Red. Yellow layer: pure yellow. Green layer: Yellow and Blue. Blue layer: Pure blue. Purple layer: Red and Blue - I used to much of both colours and it was too dark.