Line a 12-section muffin tray with paper or foil muffin cases. Put the butter, caster sugar, eggs, flour and grated lemon rind in a bowl and beat with a hand-held electric whisk until smooth.
Add the orange flower water and enough milk to give a good dropping consistency. Divide the cake mixture between the paper or foil cases.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 15–20 minutes or until risen and golden. Transfer to a wire rack to cool.
Slice the risen tops off the cakes. Mix half the icing sugar with the orange juice in one bowl and the other half with the lemon juice in another bowl. Dot a tiny amount of the relevant food colouring into each one and stir well until you have 2 pastel-coloured icings.
Pour a small amount of the orange icing over 6 of the cakes using a teaspoon to cover the surface evenly. Repeat with the remaining cakes, using the yellow icing. Decorate with the sugar-coated orange and lemon rind, pressing it on lightly. Leave to set completely.