Tsuidoku

Tsuidoku is a free color sudoku based on Graeco-Latin squares: each cell holds a unique digit-color pair, adding a 4th constraint to classic sudoku. Every row, column and box contains all 9 digits and all 9 colors, and each of the 81 digit-color pairs appears exactly once.

Play free (no account needed): https://tsuidoku.com/

iOS: https://apps.apple.com/app/id6773794537

Android: https://play.google.com/store/apps/details?id=com.tsuidoku.app

Daily puzzle shared worldwide, global leaderboard, 6 difficulty levels, 27 languages.