Why did it start?
The movement was a response to the political and socioeconomic gains made by African-Americans following the Civil War and the Thirteenth Amendment to the Constitution, which eliminated slavery. During Reconstruction, following the U.S. Civil War, black leaders in Texas and around the country gained increasing influence in the Republican Party by organizing blacks as an important voting bloc via Union Leagues and the biracial Black-and-tan faction of the Republicans.
Who labeled it?
The term lily-white movement was coined by Texas Republican leader Norris Wright Cuney, who used the term in an 1888 Republican convention to describe efforts by white conservatives to oust blacks from positions of Texas party leadership and incite riots to divide the party. The term came to be used nationally to describe this ongoing movement as it further developed in the early 20th century,including through the administration of Herbert Hoover. Localized movements began immediately after the war but by the beginning of the 20th century the effort had become national.
What were the consequences?
Conservative whites attempted to eliminate this influence and recover white voters who had defected to the Democratic Party. The effort was largely successful in eliminating African-American influence in the Republican Party leading to black voters predominantly migrating to the Democratic Party for much of the 20th century.
According to author and professor Michael K. Fauntroy, "the 'Lily-White Movement' is one of the darkest, and under-examined [sic], eras of American Republicanism.
Sources
https://everything.explained.today/Lily-white_movement/
https://www.nytimes.com/1903/02/17/archives/negroes-lose-fight-in-north-carolina-pritchards-lilly-whites.html
Black and Tan Republicans
https://www.blackpast.org/african-american-history/black-and-tan-republicans/
A Southern Family in White and Black: The Cuneys of Texas
https://books.google.com/books?id=VtaZVBagK7sC
https://everything.explained.today/Black-and-tan_faction/
https://books.google.com/books?id=DdCApZN4xjwC&pg=PA84#v=onepage&q&f=false
Hoover, Blacks, and Lily-Whites: A Study of Southern Strategies By Donald J.
https://books.google.com/books?id=YAWcOqUNRckC&pg=PA37#v=onepage&q&f=false