The following complex ions absorb in the ultraviolet-visible region of light. Which one of these shows violet colour?

$$ \left[\mathrm{CoCl}\left(\mathrm{NH}_3\right)_5\right]^{2+},\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)\left(\mathrm{NH}_3\right)_5\right]^{3+},\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}, \text { and }\left[\mathrm{Co}(\mathrm{CN})_6\right]^{3-} $$

$$ \text { What is the relationship between the structures depicted below? } $$