We report on a nuclear magnetic resonance study of the nonlinear crystal LiInSe₂. This ternary compound shows a considerable variation of its color depending on the growth or annealing conditions. Room temperature ⁷Li and ¹¹⁵In NMR spectra of as-grown and annealed single crystalline and powdered samples have been measured. Analysis of the NMR spectra, along with the X-ray diffraction and optical spectroscopy data, leads to a conclusion that the change in color upon annealing in In₂Se₃ vapor is due to a change in the number of point defects.