Copper (I) i.e. Cu1+ has electronic configuration of 3d10, which means it does not have any unpaired electron. This it cannot undergo d-d transition which leaves its salts white. Also, due to no unpaired electron, it is repelled by the magnetic field and is said to show diamagnetism.

Copper (II), i.e. Cu2+ has electronic configuration of 3d9, which means, it has one unpaired electron. So, it undergoes d-d transition that imparts colors to its salts. Also, the molecules with unpaired electrons...

Molecules having unpaired electrons show paramagnetic properties.

Transitional metals are hard, malleable, ductile, and good conductors of heat and electricity. Their common types of structures are face-centered cubic, hexagonal close packing, and base-centered cubic. Since they are of similar sizes, one can easily replace the other in a lattice structure. And they are even miscible in a molten state. So, transition metals form alloys.

In p-block elements, generally, the electrons of the valence shell only take part in bonding, therefore, in general, the cases of variable oxidation states are limited in these elements. However, in d-block elements, not only the valence shell but also the penultimate shells are incomplete, so they take part in bonding. Thus, they show many variable oxidation states than that of p-block elements.

Zn²⁺has with electronic configuration of 3d¹⁰so, it does not have any unpaired electron, and thus it cannot undergo d-d transition to impart color to its salts. But, the Cu²⁺ (3d9) has one unpaired electron that undergoes d-d transition to impart color to its salt.

A transitional element is the element, which can form one or more stable ions which have incompletely filled d orbital. Taking this definition, zinc cannot be counted as transitional element. But though copper has 3d¹⁰configuration in its ground state, it can form Cu²⁺ ion with electronic configuration of 3d⁹, so it is considered a transitional element.