This is not the easiest to find treatment on the
Yellowstone shape, but it is quite attractive! The sugar is an early version where the lid sits on an inner rim on the base. Yellowstone was introduced in 1926 and the sugar was remodeled about three years later so the lid would sit on the top rim of the bowl.
Here is the matching gravy, which was made in 1929. The Y-55 mark is the treatment number. I do not know the original name of the treatment, but I am calling it Yellow Orchid.
The following close-up shows the details of the decorative treatment. It appears that four colors were used for this decal: black, gray, yellow, and orange.