Emissivity variation with surface color?

Hello All

I'm trying to understand why the emissivity of a body change with
surface corrosion/oxidation or color. Isn't emissivity a bulk property.
I can understand why the surface roughness would affect the emitted
energy but why does the color affect it?
For instance if I painted an aluminum block (which has low emissivity)
black would I expect the emissivity or the amount of energy emitted to
change significantly?  I would appreciate any guidance on this.

Thank you.
ME Student