The Metamerism Index tools enable you to: characterize the color stability of a single color patch when changing the illuminant using a Color Inconstancy Index (CII); evaluate how two colors which are the same under one illuminant will match under another illuminant using the Special Metamerism Index (SMI); evaluate if the relationship of two color patches under one illuminant is maintained under another illuminant using two Metamerism Index (MI) methods; and judge how samples look under various illuminants (virtual light box), including two measured, or loaded from file, ambient lights. The Metamerism Index tools can accept measurements from an instrument or from a file; A CONNECTED INSTRUMENT IS NOT REQUIRED. Files for the Reference and Sample patches may contain one or more reflectance spectrums while files for the Measured illuminants MUST contain only one ambient spectrum. In the screenshot above, we measured two printed grey patches, one made from black ink only (the Reference) and the other from a mix of colored inks (the Sample). These patches can be found on page 20 of the classic book Principles of Color Technology, revised by Roy Berns (3rd ed.). We compared them using Illuminant D50 as the Reference illuminant, and a measured halogen light source (Ambient-2) with a CCT of 2851 K, close to Illuminant A as the Test illuminant. The Reference patch looks almost identical under D50 and the Ambient-2 illuminant, a color constancy which is confirmed with the low Color Inconstancy Index (CII) values computed relative to D65 (CII=0.02 between D50 and D65; CII=0.12 between Amb-2 and D65). The CII is computed independently for both the Reference and the Sample, and for each selected illuminant. The CII is computed relative to a user-specified reference illuminant (D65 by default). There is a smaller difference between the Reference and Sample patches under D50 (SMI=2.97) than between the Reference and Sample patches under Ambient-2 (SMI=4.70). The Sample is quite reddish under the Test illuminant, which is not surprising since Ambient-2, an halogen lamp , has a strong red content. The CII values for the Sample patch are much higher than those for the Reference patch. The maximum inconstancy is obtained between the Test illuminant and the CII reference illuminant (CII=4.55). The DeltaE* (SMI) color difference between the Reference and the Sample for the Reference illuminant is not zero (SMI=2,97), as it often happens in real life. In this case, the Sample L*a*b* coordinates obtained with the Ambient-2 Test illuminant were corrected as per CIE 15:2005 Section 9.2.2.3 and are shown in the (CIE15 corrected) data field; the corrected color difference, and MI, is 2.57, as shown in the MI (CIE15) data field. We also see that the MI (HunterLab) , determined from CIELAB coordinates, is 1.90. The analysis clearly shows that the Reference and Sample patches are not matched.