Wandering Wallpaper

Alternating-color patches meet a moving seam: one forecast row slides before vertical stripes are checked. Save an anchor for the alignment that matters. Tap an empty cell to paint the next color. The selected forecast row shifts one cell with wraparound; then any vertical column of four matching colors clears. Horizontal rows never score. The moving row cycles bottom to top with alternating directions. One anchor can cancel a slide; arm and cancel freely before painting. Match three stripes within eight patches. Undo restores the wall and anchor.