The same dye produces a wide range of shades between purple and red depending on how the cloth is treated/the amount used/the aging of the piece. A shift in color could very much be a gradual shift over time as styles/process change.
Adjust the acidity and you can get anything from mauve to crimson. Soda ash and citrus juice were well known even three thousand years ago.
Of course this was the dye of royalty halfway around the world to the Zapotec people even before the Aztec conquered them, but details, details.
The same dye produces a wide range of shades between purple and red depending on how the cloth is treated/the amount used/the aging of the piece. A shift in color could very much be a gradual shift over time as styles/process change.