To surrender; to no longer to support or defend a course of action.

Usage: Anastasie was aware of defeat; she struck her colors instantly. (R. L. STEVENSON.)

The flush of victory, the intoxication of success, had passed over to another: and it was he who had to strike his flag and own himself defeated. (MRS. E. LYNN LINTON.)

She was forced to strike her colors after I had defeated her in a friendly argument.