$\begin{aligned}
& \mathrm{La}^{+3}-[\mathrm{Xe}] 4 \mathrm{f}^0 \
& \mathrm{Nd}^{+3}-[\mathrm{Xe}] 4 \mathrm{f}^3 \
& \mathrm{Sm}^{+3}-[\mathrm{Xe}] 4 \mathrm{f}^5 \
& \mathrm{Eu}^{+3}-[\mathrm{Xe}] 4 \mathrm{f}^6 \
& \mathrm{Lu}^{+3}-[\mathrm{Xe}] 4 \mathrm{f}^{14}
\end{aligned}\mathrm{La}^{+3}and\mathrm{Lu}^{+3}$ do not show any colour because no unpaired electron is present.