The gold background is unusual - a little old-fashioned for a painting done in the 1470s.
It is not clear whether the present gilt surface (not original) replaced original gilding or was applied over a now-obliterated landscape, such as seen elsewhere in this room.
If the painting was gilded from the outset, this would have been specified in the contract between artist and patron.
Until the mid-fifteenth century, the intrinsic value of materials -- gold and costly pigments such as ultramarine, which is made from the semiprecious stone lapis lazuli -- accounted for much of a painting's worth.
By the time this work was made, however, the emphasis had shifted.
Patrons had come to value instead the skill of the painter, as we do today.