為相機制作閃光燈，在導航欄自定義了“閃光”圖案，希望點擊時變換圖片，但是一直沒有改變，原來是因為設置了Global Tint的顏色，所以系統會自動把圖片的顏色改為Global Tint的顏色。

解決方案，設置圖片時，添加：imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal

源碼：

- (void) setFlashOn:(BOOL)isOn
{
    if (self.captureDevice.hasFlash) {
        UIImage* flashlIcon;
        [self.captureDevice lockForConfiguration:nil]; //you must lock before setting torch mode
        if (isOn) {
            NSLog(@"set flash on");
            [self.captureDevice setFlashMode:AVCaptureFlashModeOn];
            flashlIcon = [UIImage imageNamed:@"flash_on"];
        }
        else{
            NSLog(@"set flash off");
            [self.captureDevice setFlashMode:AVCaptureFlashModeOff];
            flashlIcon = [UIImage imageNamed:@"flash_off"];
        }
        [self.captureDevice unlockForConfiguration];
        [self.navigationItem.rightBarButtonItem setImage:[flashlIcon imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal]];
    }
    else{
        NSLog(@"Sorry, this device doesn't have flash.");
    }
}

http://stackoverflow.com/questions/21252194/navigation-bar-button-item-image-color-is-different-when-design-through-xib-of-x