Staff of the Sun Magus

If you cast a copy of a card that’s a certain color, the appropriate Staff’s ability will trigger. However, if you copy a spell on the stack without casting that copy, it will not.

Most nonbasic lands don’t have basic land types, even if they produce colored mana. For example, Caves of Koilos is neither a Plains nor a Swamp. Having one enter the battlefield under your control won’t cause Staff of the Sun Magus’s ability to trigger.