An analytical method to determine how color-matching functions influence the perception of chromaticity differences is proposed. We show that, as a consequence of the observer metamerism, a metameric color-match perceived by one observer may appear to be a significant mismatch to a different observer. It is also shown that, on average, the differences between the color-matchings made by, two different observers can be estimated to be in the order of 2 CIELAB units. (C) 2009 Wiley Periodicals, Inc. Cot Res Appl, 34, 194-200, 2009; Published online in Wiley InterScience (www.intcrscience.wiley.com). DOI 10.1002/col.20493