When did US breed clubs begin actively disqualifying white-coated dogs from competition?

Starting in the 1930s

The exclusion of white-coated dogs from the German Shepherd Dog mainstream began decades ago, stemming from a belief held by some breed clubs, particularly in the United States. Beginning in the 1930s, these clubs made the decision to actively disqualify white-coated dogs from participating in competitive shows and breeding programs. The primary rationale cited for this ban was the perception that the white coloration represented a sign of weakness or constituted an undesirable deviation from the established breed standard, despite the color being present in the breed's early history. This historical action forced those who valued the white coat to pursue separate breeding lines and registries.