The first and the easiest way to pull off a rainbow is with the help of your side foot. The rainbow is basically going to help you push the ball over your back and then over the player who is facing you. This way you will be able to get past the player, and the ball will follow you from the top.
In order to pull this trick off with the help of your side foot, roll the ball (just like it will be rolling while you are running on the pitch). Right when the player is in front of you, put one foot sideways, as if it is going to block the ball. Once the side foot is right in the ball’s way, use the toe of the other foot to grab the ball between your side foot and your toe. Now take a little jump and see how the ball is going to jump over your back and then it will get past the player who is standing in front of you.
For the back heel rainbow you will require a lot of practice. You will be doing everything in the similar way, just like you did in the previous step. Roll the ball and start running with it. Right when the player is in front of you, this time block the ball’s path with the help of your heel. Right when the heel touches the ball, use the toe of the other foot to grab the ball and then push it upwards. The result is going to be the same. However, notice how the side foot rainbow was relatively easier to pull off.