LOL, thanks! Yep, basic packet buttercake is ideal - I use it all the time because the consistency is perfect. I wasn't sure if you'd use a packet one or make it from scratch. The colours you buy at the supermarket are no good - you need to buy some Wiltons Gel Colours - they are da bomb for getting vivid colours. The supermarket ones need a tonne of colouring added to get them as rich as you want them. I've used some pretty dark and light colours together and they don't relly run together that much, but you may want to use slightly more yellow batter so you have a thicker band of yellow between the red so you can tell that it's yellow kwim? Otherwise if you have a thin band of yellow it will be overwhelmed by the red. You've inspired me to make some up myself as a test for you LOL.