One Tip a Day

Continuing from yesterday, this is the application stage. 1. The third vertical line only has sky blue, so a cat must be present there. Therefore, mark sky blue in other positions with an X. 2. The rightmost vertical line only has ochre left. Since a cat must be in one of these, the protruding square next to it is an X. 3. Using the same method, mark X for green, purple, and brown, excluding the lines where only one color remains. Even just organizing this much will make it much easier to start.