Grease a 20 x 15cm/8 x 6in shallow tin.
Put the sugar and milk in a large saucepan and heat gently, stirring, until the sugar has dissolved. Bring to the boil, and boil steadily to 116°C/240°F, the soft-ball stage.
Remove immediately from the heat, and stir in the coconut. Quickly pour half of the mixture into the greased tin. Add a few drops of red food colouring to the remaining mixture, stir through and quickly but carefully pour over the first layer. Leave to cool, and mark into squares while still slightly warm. Leave to set completely, and cut into bite-size pieces.