After a search on the net, it became apparent that the Frog King is frequently used as Sunday sermon material regarding spiritual transformation in the similar manner that moralists enjoy using the lowly caterpillar that metamorphoses into the ethereal butterfly. The symbols of water, kingship and transformation are deeply embedded into Christian thought as the water usually symbolizes baptism or spiritual rebirth. Difficult to argue that the frog isn't a baptized believer if pursuing this idea. Kingship naturally relates to the Kingship of God over the universe as the transformation from sinner into saint who inherits God's kingdom.
However, is this really what the brothers were after? Were they into born-again Christianity or exploring other directions of human psyche? it seems strange that the frog gets physically transformed when he is thrown against the wall in a fit of rejection, but isn't that the key to opening the magical door of understanding? It isn't it when we finally and violently reject something unpleasant about ourselves that we are able to transform ourselves. Perhaps the frog is only a foil to the princess, two parts of a single entity. The princess although beautiful, is unpleasant, discourteous and dishonest. She has no intention of keeping any commitment with the frog and is willing to promise anything to satisfy her own selfish interests. On the outside she is beautiful, but her real nature is ugly.
The frog though is a mirror. Superficially, there's not much to be said about a frog. He gets low marks in physical beauty with a tongue that is longer than his body. He eats flies and lives in the mud. His voice is about as beautiful as the Siberian Raven's. Yet, watch a frog swim or jump, and it is lithe, flexible and beautiful in motion, and the litheness is exquisite. His performance, whether speech or bearing is charming. He shows compassion and speaks softly. Harmless, the frog is the daily breakfast of storks and other predators, unable to protect himself other than leaping to hide.
The princess though is a bully. She torments a creature that is indefensible, curses him and throws him against the wall. For what? For fulfilling her demands? For satisfying her petty whims?
But if the frog can be seen as a symbol of spiritual purity or the desire to live a spiritual life, then perhaps the ugly shape is only a reflection of the princess's true intentions and behavior, while his nature is that which she envies: hence coloring him green.
