What is Yellow Socialism?

Legal Definition
Yellow socialism has two meanings. It was an economic system proposed in 1902 by Pierre Biétry, as an alternative to the "Red socialism" advocated in Marxism. Yellow socialism was prominent until World War I, competing with Marxism for support among workers. "Yellow socialism" was also a Marxist term of abuse for all non-Marxist socialists.

After the war, the movement became absorbed into fascism, and the previously developed Austrian national socialism which from 1920 developed into Nazism.
-- Wikipedia