Not sure if this will help but it's an extract from Alejandro Yanez booklet re San Juan Nepomuceno and references Spanish Royal ships of the Trafalgar period. (
I used Google translate)
HISTORIA DEL NAVÍO "SAN JUAN NEPOMUCENO"
ordinances of the Corps of Marine Engineers:
"Ordinance of Her Majesty for the best service of the Corps of Marine Engineers in the Departments and on Board of War Ships, Year 1772" San Ildefonso, August 13, 1772.
Article 145. Each Ship will be painted equally every two years,
Frigate and other War Vessels, pontoons and Machines. The Commanding Engineer will observe that no other color is used in the exterior size, and stripes, other than yellow and black; the Entre-Bridges, and Castle with red earth, the Chambers colored porcelain and blue, unless there is a particular order from me to vary it on some Ship.
The Boats will also be painted yellow and black on the outside; inside red, aft porcelain, and her Shield as usual: the masts, Booms, and Vessels of the same colors yellow, and black, the color of the Boats.
In 1776, "His Majesty's Ordinance for the best method of preserving the stores of ships of the Royal Navy and military command of naval arsenals" was published. (Madrid Naval Museum Library, Ref. BMN-2335) In Title XXIII, Article 627 it says:
Each ship will be painted equally every two years,
frigate and other war vessels that need it. The General Engineer will observe that no other color is used in the exterior size and stripes than yellow and black: in the chambers, porcelain and blue; and in the between decks and castle the red earth, unless there is a particular order from me to vary it on a ship.
The feluccas of the General Commander of the department, Mayor and General Engineering, will be painted green; the boats on the outside, their masts, botabaras and vicheros of yellow and black and the interior of roxa unlike the stern which must be made of porcelain with the shield of my Royal Arms.