Shapes of developed silver grains strongly affects covering power and color tone of silver images in photothermographic films which are produced with a water base emulsion coating technology. We have analysed the grain shapes, the covering power, and the color tone of the developed silver images by experiments using typical photothermographic films and by simulations using Mie's light scattering theory and mathematical models for optical density. We found that color deviations from neutral grey at higher density in the silver images were dependent on the differences of light extinction efficiency factors of silver grains in the wavelength range of the visible light.