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More details on the Necklace of Fireballs (Three beads) can be found at www.dndbeyond.com
When you view a magic item while the Detect Magic spell is active, you'll see certain auras based on the schools of magic at work in the item. For a Necklace of Fireballs (Three beads), auras include:
Evocation
an ebb and flow of opposing oranges and blues