Spectradoku (Rainbow Sudoku) — Expert #1
(Published on 2. July 2026, 10:42 by Todd)
Fill the 9×9 grid so that every row, every column, and every 3×3 box contains:
- each digit 1–9 exactly once, and
- each of the nine colours R O Y G B I V A K (Red, Orange, Yellow, Green, Blue/Cyan, Indigo, Violet, Ash (grey), blacK) exactly once.
In addition, every digit+colour pair appears exactly once in the whole 81-cell grid — there is exactly one red 3, one violet 8, etc. This orthogonal-Latin-square constraint is the classical Euler 36-Officers problem generalised to 9×9.
Given clues carry both a digit and a colour (shown as coloured cells with a digit inside).
Play online: spectradoku.com
Solution code: Solution code: row 5, digits only.
Comments
on 2. July 2026, 15:08 by Todd
Hi! The site currently supports **Smart Notes mode**, which automatically marks the candidate numbers and candidate
colors in each cell — you can also use the eraser to manually clear candidates. **Manual marking of candidate numbers
and colors is still under development.
on 2. July 2026, 13:45 by PierreTombal
The spectradoku tool may need some getting used to, but I don't like it. Being able to mark multiple colours in a cell would be a big improvement.
on 2. July 2026, 11:41 by Todd
If you wanna solve this puzzle online, visit https://spectradoku.com and choose expert #80 to do it, it's very convinient. Thanks!
