Hi Liam, I didn't spot you were a new user. Welcome. You deserve a proper answer. I'm not sure when 'Pirates of the Caribbean is set, but British warships in the 18th century wore the white ensign, plus various other pennants to show which squadron they were in.So, yes you're right.
My understanding is that they wore the ensign to which the admiral commanding them was entitled. So it could be red, white or blue depending on the head honcho's rung on the navy office's ladder.
You may well be right, Teak boy. But my edition of Mr Lavery's book seems to indicate the ensign remained the same whereas the pennant changed. My computer desktop picture is the Glorious first of June and the ensign in that is a giant Union Flag.
I have been told that there were originally three navy fleets. Each wore its own colour - red, white or blue. Aparently this changed a couple of hundred years ago when the navy was re-organised into the current structure. Blue became the reservists colour, or so I heard.
So the answer depends on when the film was set.
I'm sure someone can give you a more authoritative account.
before trafalgar, every naval admiral was a member of the White, Red or Blue squadron and his ships wore the corresponding coloured ensign. Nelson was an admiral of the white so ships in his squadron wore the white ensign. he ordered all the ships in the fleet at trafalgar, regardless of squadron, to wear the white ensign as the other two could be confused with french or spanish colours if only the fly or hoist were visible during the battle. after trafalgar the rules were changed to make it permanent.
as a matter of interest, the pre-trafalgar white ensign was different to today's as it had no diagonal red cross in the union flag section. that version of the white ensign is worn today by the 'tot club' in antigua.
On a bit of a tangent...
At Trafalgar the white ensign should have incorporated the Union Flag as we know it today which was adopted after the 1801 Act of Union four years before.
The previous Union Flag without the Cross of St. Patrick had been around since 1707.
Which is why too the flag of Hawaii has the pre-1801 Union Flag version in it's state flag.
Blue was the junior squadron. Hence Patrick O'Brian's book "Blue at the Mizzen" when Aubrey first gets his flag. I seem to remember that, surprisingly, the senior squadron was the red. As someone else said, the white was adopted for the navy after Trafalgar.
The different ensigns also turn up in the Hornblower series. In "Ship of the Line" he is attached to the red squadron, and plays on the possible confusion with the French ensign since both have red flies. It's the only way that I can remember the difference between the French ensign and flag Tango.
I knew I'd seen it somewhere. I'm just re-reading Patrick O'Brian's book "Master and Commander". Aubrey tells Maturin of his ambition to become Post-captain because "up the list you go, whether you have a ship or no, all according to seniority, in perfect order - rear-admiral of the blue, rear-admiral of the white, rear-admiral of the red, vice-admiral of the blue, and so on ....". I know it's fiction, but O'Brian was very careful with his research on things like that.