According to Michele Clapton, Cersei's elaborate dresses have been telling her story since the show's first episode. Early on, Cersei's brighter clothes featured bird appliques to represent her life as King Robert's wife as a beautiful bird trapped in a gilded cage. After her husband died in a hunting "accident," Cersei returned to Lannister colors - but not for long.
Clapton, who dresses all of the Game of Thrones characters in ways that "give clues to their situation," projected the queen's rage, loss, and thirst for power, by darkening her wardrobe and adjusting her crown.
Leaning away from bright and ostentatious gowns, Cersei's life and personality are perfectly reflected later in more modest and breathtakingly detailed new looks and, what was once a tiara as gold as the Lannister lion, has now become dark and jagged crown, which was consciously chosen to look brittle to reflect Cersei's inner feelings.