We presented a method for the colorimetric assessment of cubic-shaped gemstones based on a fully controlled environment easily reproducible and its application to different specimens of quartz and topaz. The data regarding the color modiﬁcation effect of E-beam irradiation and heating treatments in those minerals was described in the CIE L∗a∗b∗ perceptual color space. A general statistical approach to the visual characterization of the internal absorbance of gemstones in a low-dimensional space, evaluated its accuracy in terms of perceptual color difference, and applied it in the computational simulation of the treatments under study was introduced. The devices and model used in the present work has been proven to be applicable for gemstones’ absorbance characterization. A low-dimensional representation of the absorbance is feasible below the limits of human perception has been proven, although physically its modelling is clearly more complex. The introduction of the g-coefﬁcients could serve as a two or three dimensional perceptual characterization of the material that is independent of the cut, hence more general than a color assessment. Our g-coefﬁcient characterization to be perceptually accurate in the absorption effect modelling has been proven and is useful for color simulation of irradiation effect in gemstones under certain situations. With the additional parameter of refractive index and a geometrical model of the gemstone, the reﬂective effects can be also simulated visually, allowing computationally for accurate image simulations of the complex appearance of cut gemstones under any circumstances.