BTDT2 "Rainbows are optical illusions. In his TOTC book, Fenn states that a searcher will be searching for HIS (Fenn's) treasure at the end of HIS (Fenn's) rainbow. The searcher in the Chase game ,to Fenn, appears to be simply a tool. A means to and end. Nothing more, nothing less. "
The pot of gold is actually at the "beginning end" of the rainbow. Everybody seems to assume that it is at the final end! The pot of gold represents alchemy = that's why it is a pot, often represented by a kettle, alchemist's tool.
That is an old secret of alchemy, hidden in front of your eyes, which you by repeating the saying, are preserving that secret knowledge for millennia, without any understanding . The rainbow is generated by the process of alchemy, used in invoking Satan = real meaning of the holy grail. The gold is used in that process, and the dust sprinkled indside the FF treasure is very likely from that process - which has already happened. Hence he calls it his rainbow