reversible obi; two-sided obi
A women's obi with different colors or patterns on each side, originally black and white, allowing two looks from one sash. Primarily a traditional garment term.
An old reversible obi came out of my grandmother's chest of drawers.
Because a reversible obi has different colors on the front and back, it expands your kimono coordination options.
From 昼夜 (day and night) + 帯 (obi), referring to the original black-and-white color scheme that suggested day and night, and by extension any obi with two contrasting sides.