The two blue panels above are the same blue (according to a spectral photometer). However they are not the same blue to you. This is an example of how you construct the colors that you see. Color is not simply surface reflectance, or surface reflectance as filtered through your three cone systems. Color is a complex construction of your Visual Intelligence that is not yet well understood. This example is a colored version of a display devised by Michael White. A related example of how you construct colors and lights is the mixed-colors demonstration.
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