Here's why:

* Copper ions (Cu²⁺) are responsible for the color. When copper metal dissolves in water, it forms copper ions.

* Hydrated copper ions (Cu(H₂O)₄²⁺) are what give the solution its blue color. The water molecules around the copper ion interact with its d-electrons, causing a specific absorption of light in the visible spectrum.

* Other factors: The shade of blue can vary slightly depending on the concentration of copper ions and the presence of other ions in the solution.