The 1st colour of the rainbow is formed by performing cunilingus on a menstruating female. The gobbled up blood is then gently spat into the mouth of one of your sexual partners. (the mouth being the previously mentioned 'pot of gold')
The 2nd colour of the rainbow is formed by performing fellatio on the male member of the group. Once climax hs been reached and ejaculated into the mouth of the fellatio performer, the contents are again spat into the 'pot of gold'.
The 3rd colour of the rainbow is formed with some gentle rimming of either partner. With some encouragement, a quick push and some previously eaten prunes, one partner shall shit in the mouth of the other. Again this is passed on to the 'pot of gold'.
The 4th colour is a nice, attractive golden colour, this helps compliment the darker browns in the rainbow. One member, (again, this member is up to the choice of all involved) shall urinate into the mouth of another member. This receiving member shall lovingly pass the contents into the 'pot of gold'.
Now that the rainbow has 4 distinct colours, it's time to enjoy it. The 'pot of gold' can enjoy the contents privately or they can share them with their chosen 'leprechauns'.
More colours maybe added.