Assessment of colour differences in silicone hand and digit prostheses: Perceptible and acceptable thresholds for fair and dark skin shades

This study addresses the dilemma of initial clinical and social acceptance of a newly fabricated silicone prosthesis in relation to its colour match to the natural skin. This was achieved by derivation of specific colour difference thresholds defining perceptible and acceptable levels of colour sensitivity. Two separate sets of 10 fair and dark shade digit prosthesis samples were each fabricated with a stepped increase in colour difference (Delta E) against the baseline hand prosthesis. Ninety individuals with normal colour vision scores were selected as colour assessors. The colour difference of each prosthesis in the two series was evaluated visually against the baseline by the assessors, using defined scores. The thresholds for perceptible and acceptable colour difference determined in this study were Delta E=0.8 and Delta E=1.8 for the fair series and Delta E=1.3 and Delta E=2.6 for the dark series, respectively. The acceptable threshold values differed from the perceptible threshold values by Delta E=1.0 for the fair-shade samples and Delta E=1.3 for the dark-shade samples. This study demonstrated that subjective visual assessment is positively correlated with Delta E values computed from colorimetric measurements for both fair and dark-shade silicone samples (p<0.001). This results shows that human subjects with normal colour vision are capable of accurately assessing colour differences. These observations emphasize the importance of subjective feedback on colour by the patient, provided the latter has perfect colour-tested vision. The study also showed that human subjects were less sensitive to perceived colour differences in darker-shade than fairer-shade samples (p<0.001). This finding seems relevant in a clinical setting involving a multi-ethnic patient population.