To develop a method for selecting a proofing substrate that closely matches a specified printing paper stock, we defined a psychometric term, Apparent Whiteness, as the perceived whiteness of a paper relative to the whitest sample in a specified illumination. In a series of visual experiments 10 observers ranked Apparent Whiteness of 39 samples in the ISO 3664 (2000) and the ISO 3664 (2009) lighting conditions. The ranking data was transformed into interval data using Thurstone's law of comparative judgment. We also measured several paper metrics - color, gloss, opacity, CIE whiteness, and OBA, to determine if Apparent Whiteness correlates with the measured paper metrics. The results indicate that the Apparent Whiteness in the ISO 3664 (2009) viewing condition has a strong linear relationship with the CIE Whiteness (M1). Thus, we are able to select a proofing substrate based on the similarity of its CIE Whiteness with the printing stock. Furthermore, we can use ?E00 (M1) to predict the numerical color match between the two substrates and use ?OBA to indicate the criticalness of lighting in the visual match between the proofing substrate and the printing stock. Finally, we verify the visual match by considering gloss, color and texture of the sample in the ISO 3664 (2009) compliant viewing booth.