Racial evaporation became harder to sustain as former colonies migrated to European metropoles

Evidence

Racial europeanization thus concerns itself overwhelmingly with racial avoidance as denial of or at least failure to acknowledge its own racist implication. But the postwar racial evaporation both deepened and became more difficult to sustain as the empire came home to the metropoles increasingly from the 1960s on. — David Theo Goldberg, The Threat of Race, 856