Monster Cake - Hulk?

My now 7 year old's birthday :) First cake choice was a racing car, ideally Formula 1 which I was completely stumped - its complex and I am not a crafter. Fortunately he jumped at this version of the Incredible Hulk - I know it looks nothing like the Hulk but for my lovely 7 year old, calling it a Monster Cake was fine, the beauty of childhood.......where the number of presents and wrapping matter more than the inside. Never spent more than £10-£15 on a present for the children, the DS's and Wii games haven't happened in our house as birthday or Christmas presents, well.....yet.
Back to the Cake, would not recommend Dr Oetker gel food colouring at all. Used many of their products loads of times, this was supposed to be better than the liquid and available from Sainsbury's so decided to give it a go. The result is a bowl of pastel green icing which looks very pretty but wont do for a monster cake. Plus I've put the whole tube of icing in, more than recommended. Will have to stick to the specialist colouring pastes I think. This time its good old Renshaw's coloured icing for a £ odd. Over and done with in half an hour (the green bit).
This is a simple square cake with a loaf cut diagonally at the corners. One of the simpler cakes I've done.
Now to sort out the weekend party and his school friends party. Going horse riding, hope its fun for the children.