Dettol is a clear liquid that gets its color from the frequencies of light that can and cannot passing through it. Mixing dettol and water creates an emulsion—a solution where small droplets of the oil are suspended in the water (the comparison to milk is apt as milk is also an emulsion of fats and proteins in water). These emulsions get their color from the scattering of light from the droplets. Here, absorption of light plays less of a role because most of the light you see has not passed through the droplets (which presumably contain the molecules that absorb light).