An extensive literature has focused on the association between human, social, and economic capital and better immigrant economic attainment, and how these characteristics contribute to stratification among members of the same group. However, few studies have explored how racialization processes contribute to these within-group differences. We examine the role of intragroup differences in skin tone in stratifying outcomes among Mexican immigrants in the early twentieth century. We create a new dataset of 1910-1940 Mexican border-crossing records that we then link to the U.S. 1940 census. We use characteristics at entry to predict income in 1940 and find that-in line with dominant assimilation theories-standard measures of capital are associated with within-group attainment differences. However, we also find skin tone to be a source of within-group stratification: being perceived as having darker skin is associated with lower subsequent economic attainment than being perceived as having lighter skin. Furthermore, whereas human and social capital transcended context to allow migrants to transfer those skills anywhere, the effect of skin tone was significant only in Texas and not in other major receiving places like California. We argue that although standard measures of assimilation typically predict later outcomes, the stratifying effect of skin tone has long been a feature of Mexican immigration.