A previous study identified a significant metamerism in the several editions of the Hardy-Rand-Rittler pseudoisochromatic plates (HRR) but did not proceed to quantify the consequences of that metamerism (Dain, 2004). Metamerism arises from two sources and is almost inevitable when a printed color vision test is reproduced in several editions. Metamerism has two consequences; these are illuminant/source-based changes in performance and changes in performance with observer (less well known) when assessing anomalous trichromats. This study addresses the effects of illuminant/source and observer metamerism on the fourth editions of the HRR. Groups of colors intended to lie on a dichromat confusion line generally remain on a confusion line when the source is changed. The plates appear to be resistant to each form of metamerism, perhaps because the features of the spectral reflectance are similar for figure color and background gray. As a consequence, the clinician needs to be less concerned about using a non-recommended source than was previously believed.
