1) In a large heavy saucepan, combine 125g of the sugar with 475ml of water and bring to a boil over high heat. Reduce the heat to medium and simmer, without stirring, until thick and amber in color. When caramelised, remove from the heat and divide among 6 individual caramel cups or ramekins. Let caramel cool to room temperature.
2) Preheat the oven to 180C/Gas Mark 4.
3) In a medium bowl, combine the remaining 100g sugar, milk, lemon zest, vanilla, food colouring, and eggs, and mix very well. Pour this mixture into the cups or ramekins; fill each until nearly full.
4) Place the creme caramel cups into a large baking dish. Make a water bath by adding water to the dish so that it comes about halfway up the sides of the cups. Bake for 45 mins. Carefully remove from the water bath, let cool to room temperature, and then refrigerate until completely chilled before serving. Serve by inverting ramekin onto a plate.