Combining food colouring with frosting allows you to create specific hues of the colour spectrum, such as grey, ranging between white and black. Making the correct colour frosting helps you portray the appearance you want for cakes, cupcakes or cookies, adding to an overall theme for birthdays, parties, showers and weddings. Grey frosting can highlight the decor of an "Over the Hill" cake; can represent a child's favourite animal such as a shark or elephant; and can create the colour of a castle for a wedding or party royalty theme. Artificial colouring does not affect the flavour of frosting and can be kneaded into fondant or stirred into icing and buttercream varieties.
Scoop the contents of white or vanilla store-bought frosting out of the container with a spoon and into a bowl.
Whisk two egg whites in a bowl if you choose to make your own fondant frosting. Add 3 cups of confectioners' sugar in 1/2-cup increments to the egg whites. Stir the sugar into the mixture until the mixture becomes smooth.
Add one drop of black or purple food colouring, depending on the hue of grey that you desire. Black food colouring produces a dark grey, versus purple colouring, which provides a light grey with a hint of purple. Another option is to combine yellow, blue and red food colouring to make grey because the three colours neutralise each other.
Stir the food colouring into the frosting or paint and knead it into the fondant with your palms and knuckles. Check the colour. Add more food colouring for a darker hue. Lighten the colour of the frosting by adding more frosting or by dropping in a white or yellow food colouring, if the grey becomes too dark.