All of the rough samples were slightly fractured and contained very few inclusions. Color was homogeneous in each stone, and most showed a subtle color change from blue under daylight-equivalent normalized light (D65) to violetish blue under incandescent light (see table 1). The authors avoid the commonly used term “color shift” (Senoble, 2010), which Manson and Stockton (1984) defined in garnets while observing the combination of two color phenomena, nowadays identified separately: classical color change with lighting, and Usambara effect (change of color with thickness). We observed that the color change is more pronounced in stones with a more saturated color. While examining numerous parcels in Yen The, we observed that most of the grayish blue spinel—and some of the very saturated blue material, contrary to our other observations—did not show any color change.