[spirochete]

Two different complexes of cobalt(II), Co(H20)₆²⁺ and CoCl₄^2- are pink and blue, respectively.  This is because the water complex is octahedral with medium strength ligands and the chloride complex is tetrahedral and has weak ligands.  The pink one is absorbing green, the blue one is absorbing red.

But equivalent Mn(II) complexes are both pink.  I wouldn't expect the chlorine complex to octahedral because it's the same charge and very similar in size to cobalt.  If it were square planar it would have a higher energy transition, but Mn(II) is not D8 (it's D5) and chloride is a weak field ligand.

Those are all my ideas but neither seem correct.

[spirochete]

By the way in case anybody needs reminding, Del_T=(4/9)Del_o, which is why I'm referring to the geometries.