My personal take on the Empress and Emperor card is that in one sense they represent the dual and complementary forces needed for the cycle of death and creation that is life: fertility and potency.
I have a slightly complex system of viewing the divine, in which God is the male force which draws us towards the transcendent and eternal, and Goddess is the female force which draws us into the world and its mortal cycles. I see both God and Goddess as having consorts, dual forces which in some ways are similar to their divine counterpart, and in other ways, move in a slightly different direction. In my cosmic casting, God's consort is the force of universal love and compassion represented in such figures as Kwan Yin Bodhisattva and Mary, Mother of Jesus. Goddess's consort is the force of chaos, wildness, and violent potency represented in such figures as the Horned God and tricksters like Coyote.
I say all this to say that I associate the Emperor with the Goddess's male side, and all that has to do with archetypes of male sexuality, and male gods with their destructive, wild, fiery power. This male force of potency is full of fiery creativity, as well as the power of destruction. Without death and destruction, there could not be new life and creation. This male force presides over the hunt and other activities which link violence with life. I also see the Emperor as a card representing male authority and dominance, direction, shaping. I think all of these ways of seeing the card work well with a quality of fire and the colors associated with it.