Question

[fef6]³- ion is colourless although iron(3) is d5 ion

Answer 1

Explanation:

Apart from the presence of unpaired electrons the d-d transitions also govern the colour of a substance in this case Fluorine being a highly stable electronegative element d-d transistion is absent

so there is no colour

other similar example (contradictory) is KMnO4

(verify class 12 ncert for further doubts)