The King's Blue (bleu du roi)
Bleu du roi (the king’s blue) was also known as gros bleu (full blue), or bleu nouveau (new blue). As was the case with other ground colors, the terminology for this shade of blue was varied and inconsistent.
Generally speaking, these terms can refer to a new blue ground color that was introduced in 1763. In some contexts, however, Savill notes that bleu du roi and gros bleu were used simply as synonyms for bleu lapis.
Although some scholars have described the bleu du roi as a shade lighter than bleu lapis, it was quite dark. As seen on the Litron Cup (gobelet litron, 1784, slide 58c), painted by Charles-Nicolas Dodin, as well as on the “Tea Canister” (boîte à thé, n.d., slide 35a), the king’s blue was a rich, dark, full-bodied blue that, in today’s terms, might be called navy blue or Prussian blue.
References: Savill 1988, 3:1174–75; Eriksen and De Bellaigue 1987, 53.