Is the brass color some sort of plating or is it the corrosion of the underlying silvery metal?
The "corroded brass" patina look comes from the Copper and Zinc, major components of the Brass alloy. It comes even when there are other components in the alloy. But the other components may suppress the copper yellow tint so make the bare metal (e.g. when polished,...) silvery looking.
So your base could well be made of such alloy: Silver when clean, but turning into brass like patina when surface corroded.
