Beat the butter, shortening, cream cheese, lemon juice and salt till they are creamed well.
Mix in the vanilla.
Gradually add confectioners sugar a little at a time while the mixer is on low. Once all the Icing sugar is added and mixed - increase the speed to medium till the mix is smooth and fluffy.
For a fluffier consistency you can add less sugar, and for a stiffer frosting add more confectioners sugar.
This cake made just enough icing to fill and frost a 3 layered 9 inch cake. You will need to make more if you want to do decorations on the cake.
Place the cake on a turntable to make it easier to frost the cake smoothly. Add about 1/2 cup of frosting between each layer of the 3 layered cake.
Apply a crumb coating on the cake and place in the fridge for about 5 minutes, if the cake is cold, the crumb coat will set faster.
Divide the remaining frosting into two. Divide one half of the frosting further into two bowls.
Mix in 4 drops of blue gel colouring into 1 small bowl (which has a quarter of the frosting) and mix well. Mix only 2 into the other small bowl (the other quarter of the frosting) and keep the remaining half white.
With a medium offset spatula liberally apply the darker frosting colour around the lower third of the base.
Apply the lighter shade in the middle part of the cake.
Apple the white frosting on the top third and the top surface of the cake.
To smoothen the extra frosting off the cake, place a straight edged scraper along the side of the cake without touching the cake, but touching the frosting. Holding the scraper firm, turn the turn-table to evenly scrape off the extra frosting and smoothen it.
Once the excess frosting is removed from the sides, smoothen the top as well.
Leave the cake to "crust" for about 10 minutes. Touch the frosting lightly to check to see if it has crusted. If not, leave it a little longer. Do not leave it for too long however since if it crusts for too long, you will not be able to smoothen it.
Place an unpatterned Viva towelette over the frosting and lightly rub over the frosting with your Fondant smoother or hand. When you remove the towelette, you will see that the Icing has become smooth. Repeat this process for the entire cake.
Alternatively you could use a heated metal spatula or cake scraper to smoothen the icing as well. However, you will need to do this before the crusting has set too much.