It should be blue before polishing. The so-called blue color is to fill all kinds of enamel glazes into the gaps of particles with a metal spatula, and then melt the powder glaze into a flat and bright glaze at a high temperature of 800 degrees. Only by repeatedly glazing and melting twice to three or four times can the glaze and copper wire be uniform, and the vessel be covered with a gorgeous, elegant and colorful coat.
So the gilded bottom can be colored. You can't judge it's not cloisonne because of this. At best, it's just poor workmanship.