Copper is a transition metal, with unfilled d orbitals.

Ground state electron configuration:   [Ar].3d10.4s1
Shell structure:   2.8.18.1
Transition metals may exhibit multiple oxidation states
(+1, +2, +3, etcÉ). 

These are not easily predicted by position in the periodic table.

Transition metals ions in aqueous solutions frequently are brightly colored, also due to d orbitals (e.g.  Cu ions are blue).