Darker skin color has been associated with higher average blood pressure in several African-derived populations in the Americas. This pattern has been interpreted as evidence of genetic, physiologic, or sociocultural mechanisms, but existing evidence does not provide an adequate means of evaluating these alternatives. This paper introduces a measurement strategy to isolate the cultural and biological dimensions of skin color, and it develops a specific hypothesis regarding the cultural significance of skin color in Puerto Rico and its relationship to arterial blood pressure. Data come from a face-to-face survey in southeastern Puerto Rico (N = 100). There is no association between blood pressure and skin pigmentation, as measured by reflectance spectrophotometry. However, the discrepancy between self-perceived color and skin pigmentation, a measure we call “color incongruity,” is associated with systolic blood pressure (SBP) through an interaction with socioeconomic status (SES) (P = 0.009). For low-SES respondents, darker self-ratings of color relative to skin pigmentation are associated with higher mean SBP. For high-SES respondents, however, darker self-ratings of color relative to pigmentation are associated with lower mean SBP. We interpret this pattern as evidence that the relationship between skin color and blood pressure is mediated by sociocultural processes, and we highlight the need for testable hypotheses and appropriate measurement operations in research on racial inequalities in health. Am. J. Hum. Biol. 17:195–206, 2005. © 2005 Wiley-Liss, Inc.