The color of an object depends on how you look at it. The color of the illumination plays a major role. The direction of the illumination and the direction of viewing relative to the object can significantly affect the color. If a measurement of color is to quantify the color appearance, the geometric and spectral conditions of measurement must simulate the geometric and spectral conditions of observation. The colorimetry of specimens that exhibit gloss or sheen require special attention to the light specularly reflected from the surface. Metals are a special case. Much remains to be done to standardize geometric conditions in colorimetry.
C. S. McCamy, C. S. McCamy,
"Geometric Considerations In Colorimetry", Proc. SPIE 0411, Electro-Optical Instrumentation for Industrial Applications, (4 November 1983); doi: 10.1117/12.935777; https://doi.org/10.1117/12.935777