Abstract In the expression of the complex refractive index of a colored colloidal system (m=m0–ik0), the value of m0 may be smaller than unity and k0 may be negative if the medium is colored. Including these cases, the values of x (corresponding to the optical density), y (scattering) and z (absorption) have been calculated for relatively small α and k0 values. The values of the apparent relative refractive index, m′, have been calculated also. These results have been discussed in detail in order to show the effect of the scattering and absorption on the scattering, absorption and apparent refractive index. It has been concluded that the data of a system in which colorless particles are dispersed in a colored medium will be practically equal to those in a colorless medium if the extinction of light according to the Lambert law is corrected properly.