Official rule text
88.2 System tiles with a green-colored back are home systems and of their unit’s “Production” abilities in the active system. faction-specific tiles. Each home system is unique to one of the a The active player may do this even if they did not move game’s factions. units or land ground forces during this tactical action.
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Source: Twilight Imperium: Fourth Edition - Living Rules Reference: Prophecy of Kings
Expansion: Prophecy of Kings
Version: 2.0
Reference: Rule 88.2