Abstract: A tristimulus colorimeter including a modified dual slope integrator digital voltmeter measures the red, blue and green light reflected from a sample and displays the same in digital form as optical density units. The colorimeter includes a light conducting probe with a diffusing member and a movable collar for blocking ambient light, and a rotating color filter wheel is synchronized with the voltmeter for effecting a continuous update of the data displayed thereby. Moreover, a color averaging method provides for prediction of the ultimate color of a mixture of two differently colored porcelains or the like especially used in the construction of artificial teeth or the like.