The Rainbow Technique is a powerful color sudoku solving method. By tracking one number across all 9 colors, you can quickly spot which color is missing — and place your next cell with confidence.
The Principle
The Principle
Each number (1-9) must appear exactly once in each of the 9 colors.
If you find a number in 8 different colors, you know which color is missing. Then find where that color goes.
Why Rainbow Works
The Rainbow Technique is possible because of Suirodoku's 4th rule: each color must contain numbers 1-9. This means every number appears exactly once in each color — creating 81 unique number-color pairs. When you track a number across all colors, you're guaranteed to find exactly 9 instances.
The number reveals the color. This is the opposite of Chromatic Circle where the color reveals the number.
Step-by-Step Example
Step-by-Step Example
Track the number 4. It appears in 8 colors — Yellow is missing!
Result: By tracking the number 4 across all colors, we found Yellow was missing and placed it!
Key Points
Key Points
When to Use It
When to Use It
- Mid-game: When many numbers are placed but you're stuck
- After basics: Use classic Sudoku rules first, then Rainbow
- Hard/Expert puzzles: Essential for difficult levels
Common mistake: Don't forget to check both number AND color constraints. A cell must satisfy all 4 rules.
Practice Now
Practice Now
The best way to master Rainbow is to practice. Start with Easy puzzles, then move to harder levels.