Dual lands (like Hallowed Fountain) are tied to both colors they have mana symbols for, and are only legal if those colors are in your commanders color identity

Julius Jumblemorph Ixalan Vona, Butcher of Magan, Tishana, Voice of Thunder, Admiral Beckett Brass, Gishath, Suns Avatar Commander 2017 Nazahn, Revered Bladesmith, Inalla, Archmage Ritualist, Mirri, Weatherlight Duelist, O-Kagachi, Vengeful Kami, Mairsil, the Pretender, Taigam, Ojutai Master Razaketh, the Foulblooded, Zur, the Enchanter (Mummys Curse), Djeru, With Eyes Open, The Locust God, Karona, False God (All the Deserts), Nicol Bolas, Neheb, the Eternal Amonkhet Oketra the True, Temmet, Vizier of Naktamun, Atogatog (Cartouches & Trials), Hapatra, Vizier of Poisons, Samut, Voice of Dissent, Rhonas the Indomitable, Hazoret the Fervent Kaladesh Block Yahenni, Undying Partisan, Nicol Bolas, Child of Alara (Five-Color Energy), Rishkar, Peema Renegade, Kari Zev, Skyship Raider, Sram, Senior Edificer Commander 2016 Breya, Etherium Shaper, Atraxa, Praetors Voice, Tymna the Weaver // Ravos, Soultender Other Commander Decks The Ultimate Golgari Deck, Anafenza, the Foremost (shutting down shenanigans), Momir Vig, Simic Visionary (no green creatures), Kytheon, Hero of Akros (Tribal Gideon), Tasigur, the Golden Fang Commander Strategy Commander Compare & Contrast: Nahiri, the Lithomancer

This is triply true in Commander, where that each opponent clause really comes in clutch
Once on the field, Liesa, Shroud Of Dusk burns the opponent for two life whenever they cast any spell