The three points of the Triforce, Wisdom, Power, and Courage, are represented by blue, red, and green respectively. There are three barrels on this card's gun, with a red shell and a blue shell loaded in two of the barrels and a third barrel without a shell (presumably fired). It is possible that the barrel without a shell originally held a green shell.
In addition, the effects of this card can also be seen as references to the three individual pieces of the Triforce. With EARTH giving the confidence to attack without fear, FIRE giving the power needed to damage your enemies, and LIGHT allowing the use of some mysterious magic.