My comment concerning phenotypic differences was perhaps an over-nuanced attempt to say that the Scotch-Irish, German, Swiss, Welsh, and English all intermarried and formed a, more or less, homogenous white population. Although there were progeny from Scotch-Irish/African and Scotch-Irish/Native American unions, these children often were considered part of the non-white population.

Regarding Native-American / Scottish/ Scotch-Irish unions, the Cherokee tribe had many members who were of mized ethnicity. John Ross, a principal chief at the time of the Removal, was 7/8 Scot.

I believe the STM has a current exhibit on this blending of ethnic groups...