Dean is flesh and earth and heavy red with blood and the flush under his skin. He indulges in all things. Dean is breakable in body but unshakable in his loyalty and determination to keep his family safe.
Castiel is ethereal and light and blue-white with an angel’s grace under his host. Castiel is unbreakable in body but all it took was one righteous man to shake his faith and be lost from the moment his grace touched the man in Hell.
They are opposites in almost every sense, and yet they still keep crashing together despite it.