Hello,
In fact it is much more complex than that.
The white "flag" was reserved for warships with the exception of Mediterranean ships which had a red "estandard" adorned with the royal coat of arms and fleur-de-lys until 1748 when they also adopted the white flag.
Merchant ships were to fly the blue flag with a white cross with "his majesty's shield".
To this we must add that there were variations depending on the situation (marks of command, honorary distinctions, "flame" of war, distinctive marks, etc.).
It's a real language that can be understood in the context where it was the only way to communicate at a distance.