Given a fixed set of viewing conditions, a colour appearance model provides a method for transforming tristimulus values to perceptual attributes correlates, and vice versa. Current colour appearance models, like CIECAM02 [1], have been developed assuming the CIE31 Standard Observer. However a general model must adequately describe the colorimetric behaviour of a large enough set of real observers. In this work we analyse the variability of the different parameters defined by CIECAM02 when different sets of colour-matching functions associated with real observers are considered. All our sets of colour-matching functions are for small-size fields (smaller than 4°). Our main goal is to evaluate the observer metamerism provided in CIECAM02 for a set of 13 real observers, when the reflectances of the 24 chips of the GretagMacbetch ColorChecker are illuminated under D65 and A illuminants.