I’m nearing completion of a sportcoat made out of a somewhat unusual piece of cashmere from Johnstons of Elgin, so I am beginning to think about buttonhole thread.
A check of this nature is sometimes challenging when the buttonholes sit on different area of colour; the normal practice of matching one colour of buttonhole thread might go out the window in favor of matching whatever stripe the buttonhole happens to sit on. I am even reminded of one garment in the YSL couture exhibit on which the finisher had even changed thread mid-buttonhole because the buttonhole straddled two areas of great contrast (yellow and black, IIRC).
The best way to know what will look best is to plan the buttonhole placement to find out where they will sit on the check, and then do a few test buttonholes on a scrap of cloth using different shades of twist. Fortunately I have that stash of vintage twist so I have a number of colours to choose from.