I think the ships in the painting are flying additional flags for ease of recognition in the battle, and there may be an element of guesswork or artist's licence. William James says of the Battle of Lissa:
Quote:
The British ships immediately formed in line ahead, with, besides the customary red ensign at their respective peaks, union jacks and ensigns, blue and red, at their foremast heads and at their different stays. Thus nobly decorated, the four ships continued working to windward to close the enemy.