amoratarse

To turn purple or bluish-purple, usually describing skin from cold, bruising, or lack of circulation — se le amorataron los labios de frío. It's the standard verb for that specific color change, distinct from general bruising vocabulary.

• Se le amorataron los labios por el frío intenso. — His lips turned purple from the intense cold.
• La rodilla se amorató después del golpe. — The knee turned purple after the blow.
• Sus manos se amorataban con cada hora que pasaba a la intemperie. — His hands kept turning purple with every hour spent out in the cold.

Using amoratarse for any bruise regardless of color — it specifically names the purple/bluish discoloration from cold or impact, not bruising in general (which can also show as other colors at different stages).