The queen accompanies the king in the King's Day parade, so Sadima gets a chance to see her:
The queen was young, lovely, her gown the color of a full moon. The sleeves were enormous, puffed out at the shoulder, but tight around her forearms. (45.46)
We're guessing Sadima notices the outfit because it's so thoroughly impractical. Who would deliberately put extra fabric in an outfit, when you could use the fabric elsewhere? And why on earth would you make a gown out of pale fabric, when obviously it'd be stained while you were working? But then, Sadima's a farm girl, and the queen has probably never worked a day in her life. She is, however, Somiss's mother.