"finally compelled to strike my colours"
by cm

HMS Iphigenia Strikes her Colours
Public DomainHMS Iphigenia Strikes her Colours - Credit: Pierre Julien Gilbert
Striking the colours means surrendering

In international law, naval ships are required to fly their national flag or ensign ("colours") before commencing hostilities.  If the colours are taken down during battle, it signifies surrender.  Hence, particularly defiant combatants will "nail the colours to the mast" to signal a refusal to surrender.

Hoisting a white flag signifies a request for a truce, not an indication of surrender as is commonly believed.