51 cards where the card is tagged “colourless-matters”

Abstruse Archaic (Commander Masters #712)
Ancient Stirrings (Double Masters #151)
Barrage Tyrant (Battle for Zendikar #127)
Breaker of Creation (Modern Horizons 3 #1)
Calamity of the Titans (Commander Masters #713)
Conduit of Ruin (Battle for Zendikar #4)
Cultivator Drone (Oath of the Gatewatch #42)
Darksteel Monolith (Commander Masters #743)
Dominator Drone (Battle for Zendikar #92)
Dust Stalker (Battle for Zendikar #202)
Echoes of Eternity (Modern Horizons 3 #4)
Eldrazi Aggressor (Oath of the Gatewatch #95)
Eldrazi Mimic (Oath of the Gatewatch #2)
Eldrazi Temple (Commander Masters #992)
Eye of Ugin (Modern Masters 2015 #242)
Flayer Drone (Oath of the Gatewatch #148)
Forerunner of Slaughter (Battle for Zendikar #204)
Forsaken Monument (Commander Masters #950)
Ghostfire Blade (Khans of Tarkir #220)
Grizzled Angler // Grisly Anglerfish (Eldritch Moon #63)
Grizzled Angler // Grisly Anglerfish (Eldritch Moon #63)
Gruesome Slaughter (Battle for Zendikar #9)
Herald of Kozilek (Battle for Zendikar #205)
Infernal Reckoning (Core Set 2019 #102)
It That Heralds the End (Modern Horizons 3 #9)
Kozilek's Sentinel (Battle for Zendikar #129)
Liberator, Urza's Battlethopter (The Brothers' War #237)
Molten Nursery (Battle for Zendikar #130)
Mystic Forge (Commander Masters #964)
Nettle Drone (Battle for Zendikar #131)
Omarthis, Ghostfire Initiate (Commander Masters #708)
Reaver Drone (Oath of the Gatewatch #76)
Ruination Guide (Battle for Zendikar #64)
Ruins of Oran-Rief (Commander Masters #1023)
Sanctum of Ugin (Battle for Zendikar #242)
Shrine of the Forsaken Gods (Murders at Karlov Manor Commander #292)
Skittering Cicada (Commander Masters #717)
Skitterskin (Battle for Zendikar #97)
Sky Scourer (Oath of the Gatewatch #78)
Spreading Plague (Invasion #125)
Swarm Surge (Battle for Zendikar #100)
Thought Harvester (Oath of the Gatewatch #48)
Tide Drifter (Battle for Zendikar #67)
Titan's Presence (Commander Masters #810)
Tomb of the Spirit Dragon (Commander Masters #1048)
Ugin's Construct (Fate Reforged #164)
Ugin's Labyrinth (Modern Horizons 3 #233)
Ugin's Mastery (Murders at Karlov Manor Commander #53)
Ugin, the Ineffable (Commander Masters #811)
Vannifar, Evolved Enigma (Murders at Karlov Manor #241)
Vile Aggregate (Battle for Zendikar #137)
Zhulodok, Void Gorger (Commander Masters #704)

The message was clear to Sorin—time to search for something else.