Good, Jeskai Control resolved to a Pioneer archetype. Let me check its card list in detail to see if it runs a 4th color.
No, the Jeskai Control archetype in the database is a true three-color (White-Blue-Red) deck, not a 4c version. Looking at the card list from the last ~3 months in Pioneer, every list runs exclusively Jeskai colors: the mana base is built around Hallowed Fountain, Steam Vents, Sacred Foundry, and Raugrin Triome, with no lands or spells touching a 4th color (Black or Green). Key spells like No More Lies, Lightning Helix, Consult the Star Charts, and Get Lost are all squarely WUR.
One deck in the sample (33% of entries) does include Beza, the Bounding Spring, which is a Green card, but it appears to be a singleton one-of and is present in only one list. The other two decks show zero Green or Black cards. So the archetype as registered and tracked in tournament data is a clean Jeskai build.
Sources: Data from 3 Pioneer Challenge 32 events on MTGO (July 2026), 100% MTGO coverage.
https://www.mtgo.com/decklist/pioneer-challenge-32-2026-07-1112847134
https://www.mtgo.com/decklist/pioneer-challenge-32-2026-07-0512846501
https://www.mtgo.com/decklist/pioneer-challenge-32-2026-07-0312846469