Explanation:
PtCl₄^2- is a colourless compound even though it contains a transition metal, platinum, in its structure. This can be explained by considering the electronic configuration and bonding in the compound.

Electronic Configuration:
- Platinum (Pt) in its +2 oxidation state has the electronic configuration [Xe] 4f¹⁴ 5d⁸ 6s⁰.
- The presence of filled d orbitals (d⁸) in the Pt²⁺ ion results in the absence of d-d transitions, which are responsible for colour in transition metal compounds.

Bonding:
- In PtCl₄^2-, platinum is surrounded by four chloride ions in a square planar geometry.
- The bonding in PtCl₄^2- involves the donation of electron density from the chloride ions to the empty d orbitals of the platinum ion, forming coordinate bonds.
- Due to the strong ligand field created by the chloride ions, the d orbitals of platinum split into higher energy (e_g) and lower energy (t_2g) sets.
- The energy required for electronic transitions between these split d orbitals falls outside the visible light range, resulting in the absence of color in the compound.

Conclusion:
- The lack of d-d transitions, coupled with the strong ligand field effects in PtCl₄^2-, leads to the compound being colourless despite containing a transition metal ion.