Income-based disparities in health and access to medical care are persistent features of population health in the United States. Differences in health care provider networks of public and private payers may contribute to these disparities. We analyzed All Payer Claims Data from 2012-2016 for the state of Colorado to characterize overlap in primary care providers serving Colorado residents with Medicaid and commercial insurance. We found a small number of providers accounted for a disproportionately large share of Medicaid beneficiaries and a high degree of primary care segregation in primary care service areas. From 2012 to 2016, the share of adults with Medicaid insurance increased (24% in 2012 vs. 40% in 2016) and primary care segregation decreased (dissimilarity index: 71% in 2012 vs. 59% in 2016). The percentage of beneficiaries with Medicaid insurance increased sharply in the year following Medicaid expansion but primary care segregation decreased smoothly during the study period.