* Copper nitrate (Cu(NO3)2) is typically blue or greenish-blue in its hydrated form. This is due to the presence of the copper(II) ion (Cu²⁺), which absorbs certain wavelengths of light and reflects others, leading to the blue color.

* Sulfur (S) is a yellow solid. Its color arises from the way its electrons absorb and emit light.

It's possible you're confusing sulfur with copper sulfide (CuS), which is black. This compound is formed when copper reacts with sulfur.

It's important to remember that chemical compounds have unique properties, including color, based on their chemical structure and bonding.