Line a 9” x 13” deep baking pan with baking parchment.
Place the sugar and milk into a heavy based saucepan fitted with a sugar thermometer and heat gently, giving it a stir from time to time until the sugar has dissolved.
Keep heating until the mixture starts to bubble rapidly. Boil for about 10 minutes, stirring constantly until it reaches soft ball stage on a sugar thermometer (240F). You can also test this by dropping a little of the mixture into a cup of cold water using a teaspoon If it forms a ball and is soft to the touch then it is ready. It is very important to get to this temperature otherwise your fudge will not set.
Add the rest of the ingredients and beat well until smooth and thick. Pour into the prepared tin and leave to cool completely, preferably overnight.
Turn the fudge out onto a board and cut into the required shapes.
Melt the coloured candy melts in the microwave, one at a time, stirring until smooth. Add a little vegetable shortening to make them thin enough to dip the fudge into.
Dip the fudge shapes into the candy melts and leave to set on a wire rack.
Melt the black candy melts and scoop into the small piping bag. Pipe lines onto the fudge to separate the blocks. Leave to set.