Why copper sulphate solution in water does not show Tindall effect but a mixture of water and milk shows?

The scattering of light by colloidal particles is known as Tyndall effect.

Milk is a colloidal solution which appears to be homogeneous but actually it is heterogeneous. The particles of milk are big enough to scatter light. Hence milk shows Tyndall effect.

The copper sulphate solution in water is a true solution which is homogeneous. The particles are very small and do not scatter light. Hence copper sulphate solution in water does not show Tyndall effect.