Each puzzle is a 9×9 grid. Instead of the numbers 1–9 you place nine pastel hues so that every row, every column, and every 3×3 box contains each hue exactly once.

Tap a cell, then tap a hue from the palette to place it. Long-press or use Notes mode to pencil-mark candidate hues in a mini 3×3 inside the cell; notes clear automatically when you place a hue.

Conflicts are flagged with a red ring and a gentle shake (you can set this to strict, lenient, or off in Settings). Stuck? The hint button fills the most logical next cell.

I'm colour-blind — can I still play? — Yes. Turn on Settings → Patterns to draw a distinct shape (stripe, dot, ring, chevron…) on each hue so they're distinguishable without relying on colour.

Where is my progress stored? — In a local database inside the app's private storage on your device. It never leaves your device, and uninstalling the app removes it.

How do I start over? — Settings → Reset progress deletes all completed levels and the saved game (with a confirmation first).

What are the difficulty tiers? — Gentle, Calm, Focused, and Deep. Each tier gives fewer starting clues and requires progressively harder solving techniques.

Which tiers are free? — Gentle and Calm are free to play. A single one-off "Full Game" purchase unlocks Focused and Deep permanently.

I bought the unlock on another device — how do I get it here? — Open Settings and tap "Restore purchases".

Does Huedoku need the internet? — No. All 400 puzzles ship inside the app; it works fully offline and makes no network calls beyond the App Store purchase and restore.