What is behind the repeating "white van" conspiracies?

Baltimore: https://www.baltimoresun.com/politics/bs-md-pol-young-white-vans-20191203-bfx466ytnjgkxmslpxrh2kriba-story.html The mayor of the city started this one. Snopes calls this false

Tennessee: https://www.oxygen.com/crime-news/white-van-hoax-gjuandell-effinger-favian-miguel-murder-baltimore-facebook This one resulted in murder

Washington D.C https://www.wired.com/2017/05/mike-obsorne-white-vans-black-suburbans/

What is this all about? Why the white van. Why not a blue van or a white pick up truck? Why any of this at all?