40 cards where the set is “khansoftarkir” and the number of colors is 3

Anafenza, the Foremost (Khans of Tarkir #163)
Narset, Enlightened Master (Khans of Tarkir #190)
Sidisi, Brood Tyrant (Khans of Tarkir #199y)
Surrak Dragonclaw (Khans of Tarkir #206)
Zurgo Helmsmasher (Khans of Tarkir #214)
Abzan Ascendancy (Khans of Tarkir #160)
Ankle Shanker (Khans of Tarkir #164)
Avalanche Tusker (Khans of Tarkir #166)
Butcher of the Horde (Khans of Tarkir #168)
Crackling Doom (Khans of Tarkir #171)
Duneblast (Khans of Tarkir #174)
Flying Crane Technique (Khans of Tarkir #176)
Ivorytusk Fortress (Khans of Tarkir #179)
Jeskai Ascendancy (Khans of Tarkir #180)
Kheru Lich Lord (Khans of Tarkir #182)
Mantis Rider (Khans of Tarkir #184)
Mardu Ascendancy (Khans of Tarkir #185)
Rakshasa Vizier (Khans of Tarkir #193y)
Sage of the Inward Eye (Khans of Tarkir #195)
Savage Knuckleblade (Khans of Tarkir #197)
Siege Rhino (Khans of Tarkir #200)
Sultai Ascendancy (Khans of Tarkir #203y)
Temur Ascendancy (Khans of Tarkir #207)
Trap Essence (Khans of Tarkir #209)
Villainous Wealth (Khans of Tarkir #211)
Abzan Charm (Khans of Tarkir #161)
Armament Corps (Khans of Tarkir #165)
Bear's Companion (Khans of Tarkir #167)
Jeskai Charm (Khans of Tarkir #181)
Mardu Charm (Khans of Tarkir #186)
Mardu Roughrider (Khans of Tarkir #187)
Sultai Charm (Khans of Tarkir #204)
Sultai Soothsayer (Khans of Tarkir #205)
Temur Charm (Khans of Tarkir #208)
Warden of the Eye (Khans of Tarkir #212)
Abomination of Gudul (Khans of Tarkir #159)
Abzan Guide (Khans of Tarkir #162)
Efreet Weaponmaster (Khans of Tarkir #175)
Ponyback Brigade (Khans of Tarkir #191)
Snowhorn Rider (Khans of Tarkir #201y)

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