We don't have synonyms for grisailles yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are grisaille.
(n) :
(art) In painting, a method of working which employs only varying values of gray to create form. Often a preliminary step in a fully colored painting.
(n) :
(art) In painting, a method of working which employs only varying values of gray to create form. Often a preliminary step in a fully colored painting.