The color of $[\mathrm{Ti}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6{]}^{3+}$is due to

$[\mathrm{Ti}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6{]}^{3+}$ is colored due to  d-d transition.

The d-d transition is the absorption of light energy to go from lower energy d orbitals set ${\mathrm{t}}_{2\mathrm{g}}$ in the octahedral complex to higher energy d orbitals.