Separate your fondant into two equal parts. How much fondant you are using depends upon what you are going to use it for. If you just want to decorate the cake or pastry, use smaller amounts of fondant; however, if you want to cover your cake with the marbled fondant then use a large amount.
Roll each portion to make a ball.
Dip a clean toothpick into the gel colour and push it into one ball. Make sure there is a very small amount of gel on the toothpick. Gently knead the fondant to evenly mix the gel colour.
Dip another toothpick into an alternate colour and repeat the above step for the second ball.
Roll out each fondant ball into a long rope as thick as a roll of quarters. Place the two snake-like ropes side by side and twist together to give them a spiral shape, just like a breadstick. If you are using more than two shades, braid them all.
Fold the twisted fondant in half and squeeze it gently to allow the colours to fuse. Twist and fold the fondant again until the desired shade and appearance has been achieved.
If you do not want the colours to mix completely, twist and fold fondants just a few times. However, even if you want a more combined look, do not over-twist and fold, it may cause the colours to fuse completely, making one solid colour.
Place the twisted fondant on a non-stick surface, flatten it out with the help of a rolling pin and apply it to the surface of the cake.