It is commonly known that when zinc metal is placed in a solution of copper(II) sulfate, a displacement reaction occurs, and elemental copper is deposited onto the decomposing zinc metal. A practical demonstration of this shows the zinc turning black from the deposited copper.
My question is, why is the deposited copper black? I thought metallic copper was red. Moreover, the dark color can be seen instantaneously, meaning the color cannot result from copper oxidizing.
I recently read a paper that claimed the copper is deposited in the form of plasmonic nanoparticles, and said nanoparticles display excellent solar absorption (and low thermal emittance, in fact). Any ideas?