10 cards where the number of colors is 4

Atraxa, Praetors' Voice (CM2) Breya, Etherium Shaper (C16) Dune-Brood Nephilim (GPT) Glint-Eye Nephilim (C16) Ink-Treader Nephilim (GPT) Kynaios and Tiro of Meletis (C16) Saskia the Unyielding (C16) Witch-Maw Nephilim (GPT) Yidris, Maelstrom Wielder (C16) Yore-Tiller Nephilim (GPT)

This search is finished. Now the real work can begin.