What would British colonists known or practiced? I've heard a lot of claims from the modern occult community about the use of Psalms as charms, and read about the scholarly debate on the extent of belief in spirits in Britain at the time (for example Margaret Murray's debunking and Wilby's book "Cunning Folk and Familiar Spirits: Shamanistic Visionary Traditions in Early Modern British Witchcraft and Magic".)
I'm curious if there's an identifiable tradition of folk magic amongst British colonists, especially since there's lingering traditions like dowsing or wart charming that may have come out of such beliefs.
Interesting question, but it's impossible to answer given your terms. "Folk magic" isn't a helpful way for an historian to think about religious practices, because that's not how anybody employing them would have thought about them. What I think you're asking is "what aspects of early modern British protestant Christianity made sense to people in the seventeenth and eighteenth centuries but are no longer practiced today?"
If that's the case, then the most obvious and important answer is witchcraft. Whether or not anybody "practiced" witchcraft is debatable, but consensus or mainstream protestant British opinion in the seventeenth century was that it was very much real. That it was something to be opposed made it no less real to them.
If you're interested in how traditional ritual practice overlapped with British Christianity, another really good source is Ronald Hutton's The Stations of the Sun: A History of the Ritual Year in Britain (Oxford, 1996).