This question comes specifically from an IB Chemistry HL Paper 1 in May 2018 TZ1, namely question 8.
Which complex has the greatest d orbital splitting?
It gives 4 Complexes $\ce{[Fe(H_2O)_6]^{2+}}$, $\ce{[Fe(H_2O)_6]^{3+}}$, $\ce{[Co(H_2O)_6]^{3+}}$, $\ce{[Cr(NH_3)_6]^{3+}}$ and it says that they give the colours green, orange, blue and violet respectively.
Initially I thought that the answer would be $\ce{[Cr(NH_3)_6]^{3+}}$ because it gives the highest energy light, being violet. However, the answer is given as $\ce{[Fe(H_2O)_6]^{3+}}$, why is this?