Ti [Ti(H2O)6]3 is in +3 oxidation state and
Sc in [Sc(H2O)6]3 is in +3 oxidation state.
The outer electronic configuration of Sc, Ti and the corresponding trivalent ions are
Sc21 : 3d1 4s2 Sc3+ : 3d0
Ti22 : 3d1 4s2 Ti3+ : 3d1
Since there is no electron in 3d orbitals of Sc d-d transition is not possible hence [Sc(H2O)6]3+ is colourless. But Ti3+ in [Ti(H2O)6]3+ has one electron in 3d orbitals hence d-d transition is possible hence it is coloured.