Ions which have unpaired electrons electrons exhibit colour in solution. 

\(Ti\) \(^{3+}\) has an outer electronic configuration of \(4 s^{0} 3 \mathrm{d}^{1},\) i.e., \(1\) unpaired electron. 

Thus its solution will be coloured.

\(\mathrm{S} \mathrm{c}^{3+} \rightarrow \mathrm{d}^{0}\)

In case of \(\mathrm{La}^{3+}, 4 \mathrm{f}^{0}\) configuration is present and in \(\mathrm{Lu}^{3+}, 4 \mathrm{f}^{14}\) is present. 

So, there is no possibility of \(f-f\) transition, hence these ions do not appear coloured.