Statement of problem. Color deterioration of silicone prosthetic elastomers affects the life expectancy of facial prostheses in a service environment. Purpose. This study investigated the color stability of 3 nonpigmented silicone elastomers (Silskin 2000, Elastosil M3500, Ideal) exposed to outdoor weathering for 1 year. Material and methods. A tristimulus colorimeter was used to evaluate the color differences (ΔE*) of the silicone elastomers every 2 months. Ten disk-shaped specimens for each material were tested. Data were analyzed with a repeated measures ANOVA and Student-Newman- Keuls test at a significance level of α=.05. Results. All silicone elastomers showed visually detectable, mean color differences (ΔE* > 2.0), that ranged from 2.13 to 3.98. Silskin 2000 showed greater color differences ( P <.05) compared with Elastosil M3500 and Ideal, which showed similar behavior ( P >.05). Conclusion. Outdoor exposure of silicone facial elastomers for 1 year resulted in visually detectable color differences. Duration of exposure and silicone elastomer were significant factors that affected color stability. Silskin 2000 was significantly less color stable than Elastosil M3500 and Ideal, which were not statistically significantly different from each other. (J Prosthet Dent 1999;82:447-50.)