Not fair Marc
The only thing I can find on color above the waterline is from the Public Records Office Adm 198/2507 and a little in contracts. This is shown on page 240 of Goodwin's
The Construction and Fitting of the English Man of War.
From the PRO July 18, 1715
You are to use good husbandry in painters works and not to refresh after to the weather than once a year or two and the inboard works that are from the weather. Only upon Rebuilding and Great Repairs or after a long foreign voyage when a ship hath not been painted in the usual colour yellow and ground black, and that both inside and out be of plain colour only except such part of the Head, Stern, and Galleries as are usually friezed and that ships boats be painted only as the painters contract directs and not otherwise though even at private charge.
I checked several contracts that give some information. The
Artois class contract at RMG (which would also be for Diana) is missing some pages but the following are from contracts in 1781 and later and all have similar wording.
The Bottom to be painted or payed, as shall be directed, with tar boiled to a strong Consistence, and to paint the sides from the Wales upwards with three good Coats of Paint, the last Coat to be of a Yellow Cast.
To treble paint the Ship within and without Board with good Oil Colours, and in like Manner the Great Cabin, Steerage, and all the Cabins, Rails, Stantions, Ladders, Gratings, Gangways, Bulkheads, Capstands, Upper deck beams, and Knees, and all the Work in Wake of them, and without board for finishing and compleating the Hull of said Ship, shall be done in a Workmanlike Manner, equal in all respects to those of His Majesty’s Ships of the like Quality in the King’s Yards.
From and article by RJB Knight "The Introduction of Copper Sheathing to the Royal Navy" in the Mariner's Mirror of the Society of Nautical Research Volume 59 page 304: By 1779 below the waterline the hulls were triple painted with white lead to prevent any galvanic action between the copper sheets and iron bolts they otherwise come in contact with. '
There was proof that not having the hull payed before coppering when four ships of the line were lost due to the corrosion of hull bolts. For our purposes, the coating under the copper will not be seen so probably makes little sense to apply it at all before coppering.
I could not find any contractural information on painting the wales black or mention of painting the black strake on top of the main wales.
If the wood on the ships was not painted it would be the color of oak, not sapele or walnut.
Allan