(There is also a neutral color used by artifacts, well come back to that.) Each color has a theme long established: White: Peace, law, structure, selflessness, equality Blue: Knowledge, deceit, caution, deliberation, perfection Black: Power, self-interest, death, sacrifice, uninhibitedness Red: Freedom, emotion, action, impulse, destruction Green: Nature, wildlife, connection, spirituality, tradition (From the Color page of the MtG Fandom wiki.) Colors form a complex structure of alliances and enmities based on their relative positions in the color pie: for example, white is adjacent to blue and green in the wheel, and opposite to red and black
That can get you all 3 cards, but it comes with a much harder restriction, as it really wants you to be in a Lesson archetype
In a fun turn of events, it seems like Grixis upkeeps is a lot more of an enchantment deck than I expected, so here are some all-stars that work great in both Obeka and The Ninth Doctor
Cards like Archangel of Thune and Heliod, Sun-Crowned can provide extra counters to make this cost less steep
Selvala, Heart of the Wilds $4.99 Selvala isnt powerful enough to crack the roster of Legacy Elves or anything, but shes an auto-include in nearly every green-based Commander ramp deck out there