The cuvette wall and sample thickness can significantly affect the results of spectral measurements of the suspension in a hardly predictable manner. We propose an approach to accounting for the cuvette wall thickness in the limiting case of thick walls and a thin sample layer when calculating the diffuse reflectance and transmittance using a one-dimensional radiative transport equation. The comparison with the experimental results for a model colored suspension is made. It is shown that with the cuvette wall influence taken into account it becomes possible to account for the fact that the scattered light fails to fully fit within the integrating sphere. There is good agreement between the experimental and calculated spectra provided that the scattering anisotropy factor is predetermined in a wavelength range where the pigment used does not absorb light.