The Brooklyn Museum has a large collection of these paintings, and has exhibited and published them.
This painting is tiny, just 8 x 11 1/2 inches. (20.2 x 29.2 cm). It's painted in opaque watercolor, which lends itself to detailed handling and delicacy (those faces are less than a half inch tall). The yellow color of the robes suggests the luxurious contrast to the common peasant costumes, and conveys the status of the magi as astronomers.