Stronghold Confusion

Why is the ‘Red Castle’ marked with a blue flag at the start of the match, and the ‘Blue Castle’ marked with a red flag at the start of the match?

If this really is the case, [for example] if the red alliance captures the blue alliance’s castle, both towers would have blue flags, making it seem like blue won the match, when in actuality, red won. (And vice versa)

Image from manual is attached.

I posted this in a different thread, but I think the problem is on top down view, the red castle’s red flag is “up” and the blue is “down”. What we’re seeing is the flag that is “down” (blue) on the red side.
If you use this assumption, all the figures in the manual are right.

So red flag up on red side at start, etc.

I would agree with this statement. If you look really closely you can see that there is a small darker dot towards the playing field side of the castle. My guess is that this is meant to represent the flag pole that is upright.