Instead of the usual four colors, this one has a fifth (in the center square). The center square belongs to both the region that goes through it horizontally and the region that goes through it vertically. The fifth color is also the average of the two colors that correspond to those regions.
The official rules:
- The digits 1 through 9 appear in each row and each column exactly once.
- Digits in each shaded region must add to the indicated sum.
- Squares with multiple colors contain a number that’s used in the sum for adjacent regions of each of those colors.
- Remember: numbers can repeat within a shaded region if that doesn't violate the first rule.