Diagonally touching tiles do not join the flood in a color fill game — only horizontal and vertical edge-neighbors establish connectivity, so two tiles that meet at a corner stay separated even when they share the same color. In a color fill puzzle, the controlled region is always the monochromatic component connected to the top-left starting tile through a path of orthogonal neighbors, which is why a same-color tile sitting diagonally above another one can look like it should be reachable when it actually is not. The rule is defined the same way by the formal Flood-It complexity literature (Arthur, Clifford, Jalsenius, Montanaro, and Sach, The Complexity of Flood Filling Games) and by Simon Tatham's reference Flood documentation (Portable Puzzle Collection — Flood): a move recolors the region connected to the origin using only up, down, left, and right adjacency, and corner contact alone never expands that region. Once you internalize that single rule, the rest of the puzzle is about choosing the sequence of colors that turns the entire grid into one connected monochromatic board before the move counter runs out, and the fixed 5 by 5 Flood It challenge is the cleanest place to practice it.
The Orthogonal-Only Connectivity Rule
Every Flood It move starts from the same place: the outlined region in the top-left corner of the board. When you pick a color, the entire monochromatic region connected to that starting tile — every cell sharing its color and reachable from it by walking up, down, left, or right — gets recolored to your choice. As soon as that recoloring finishes, any neighboring tiles that were already showing your chosen color get pulled into the region, because they are now orthogonally adjacent to a tile of their own color. That second step is the only way new tiles ever join your region during the same move.
Two tiles that share a corner but not an edge never satisfy this condition. They have no horizontal or vertical step between them, so neither becomes orthogonally adjacent to the other regardless of how the colors line up. The rule is stated the same way by both reference sources — the Flood-It complexity paper defines a move as changing "the monochromatic component connected to the top-left tile," and Simon Tatham's reference implementation describes the same procedure without invoking diagonal adjacency at any point. Corner contact is purely a visual coincidence in this game.
Why Same-Colored Diagonals Look Connected but Aren't
The confusion usually starts when two matching tiles sit diagonally next to each other. They appear close, they show the same color, and your eye instinctively treats them as one shape. The game counters that intuition in two ways. First, every controlled tile is outlined on the board, so the boundary of your region is drawn explicitly instead of inferred from color — you can see exactly which tiles are inside and which are still outside, even when a same-colored tile sits just outside the outline. Second, the controlled region can bend around the board and can contain many tiles, but every one of those tiles still shares a same-color orthogonal path back to the top-left origin, which is the only connectivity that matters for expansion.
A diagonal pair will only join once a chain of orthogonal neighbors forms between them through tiles you have already claimed. Until that chain exists, the corner tile is genuinely unreachable from the top-left, no matter how many moves you make, because there is no horizontal or vertical path connecting them through the controlled region. That separation is what makes the puzzle interesting: visually obvious shortcuts are blocked, and the only way to claim a corner tile is to wrap an orthogonal route around to it from the other side.
| Connectivity condition | Whether it joins the flood | Why |
|---|---|---|
| Shares a horizontal edge with a controlled tile | Yes | The step is purely orthogonal in the same row. |
| Shares a vertical edge with a controlled tile | Yes | The step is purely orthogonal in the same column. |
| Touches a controlled tile at a corner only | No | No horizontal or vertical step exists between the two cells. |
| Same color as a controlled tile but separated by a different-colored row or column | No | No orthogonal chain of same-color tiles links them yet. |
How to Play Flood It on a 5x5 Board
- Start from the outlined top-left tile and choose a different color. The top-left cell of Flood It begins as Blue (label 0), and the outlined region is just that single tile. Pick any of the other three colors — Coral, Gold, or Teal — using the four color buttons below the board, the number keys 1 through 4, or the arrow keys to move a cursor and Space to confirm. The recoloring will pull in every same-colored tile that is orthogonally connected to the start.
- Watch the region bend around the board and use Undo if your choice stalls. Each successful move appends one color letter to the move history. If a color does not reach as far as you hoped, press Delete or Backspace (or click Undo color) to remove the last selection; the game deterministically replays the remaining history from the original starting board, so undoing never corrupts state.
- Keep expanding until all 25 tiles form one connected monochromatic board. Only horizontal and vertical neighbors count, so plan routes around the grid rather than through corners. You have at most eight moves to finish, and the move counter ticks once per confirmed color choice.
- Press Enter or choose Check board to score exactly 1,000 points. The check has to happen at or before move eight, and the board must be fully monochromatic. Any earlier check counts as an incomplete attempt and does not add a mistake, so you can inspect your progress freely until the limit is reached.
The Fixed Starting Layout and the Eight-Move Target
The Flood It board never changes between sessions, which is unusual for a color fill game and is part of why its behavior can be audited exactly. The disclosed row-major starting board is 01231 / 11320 / 20231 / 32102 / 13023, where each digit maps to one of the four displayed colors: 0 is Blue, 1 is Coral, 2 is Gold, and 3 is Teal. That gives five Blue tiles, seven Coral tiles, seven Gold tiles, and six Teal tiles, with every row distinct. Restart always restores this exact arrangement rather than generating a new random seed.
The eight-move limit is not a guess. An independent breadth-first search treats each complete board coloring as a state, tries each of the three colors different from the current top-left color from every state, performs a separately written flood operation, serializes the result, and visits each distinct board only once. That exhaustive exploration finds 415 reachable boards, no solved board at depths zero through seven, and the first monochromatic board at depth eight. If your goal is to finish inside the limit, eight is the floor you are working against.
Three Verified Routes to a Perfect Finish
A second independent enumeration checks every legal color sequence of exactly eight moves and finds three that all reach a monochromatic board. The game accepts all three — it does not compare your play against one memorized answer, and you are free to discover any of them. The numeric labels below map directly to the colors shown in the interface, with 0 = Blue, 1 = Coral, 2 = Gold, and 3 = Teal.
| Route | Move sequence (numeric IDs) | Move sequence (interface colors) |
|---|---|---|
| A | 1-0-2-3-1-0-2-3 | Coral, Blue, Gold, Teal, Coral, Blue, Gold, Teal |
| B | 1-3-2-1-0-2-3-1 | Coral, Teal, Gold, Coral, Blue, Gold, Teal, Coral |
| C | 1-3-2-3-1-0-2-3 | Coral, Teal, Gold, Teal, Coral, Blue, Gold, Teal |
To anchor what a single move does on this specific board, follow the first step of any route. The initial controlled region is only cell 0, which is Blue. Choosing Coral on move one recolors that tile and connects it to the Coral tiles immediately to its right and below, then continues through their orthogonally connected Coral neighbors. The controlled indices after that single move become 0, 1, 5, and 6. A separate Coral tile elsewhere on the board stays outside the region until a later expansion reaches it, because no orthogonal path from the start reaches it yet. Watching how a single recolor extends one step at a time through the grid is the most direct way to see why diagonals are inert: the flood literally walks a path, and a corner step is not on the path.
Controls, Undo, and the Two-Strike Check Policy
Pointer play uses four large color buttons below the board; each button exposes its color name, the current-color state, and the keyboard selection to assistive technology. Keyboard play is fully equivalent: the arrow keys cycle the color cursor, Space confirms the selected color, and the number keys 1 through 4 choose Blue, Coral, Gold, or Teal directly. Delete or Backspace undoes the latest color, and Enter checks the board. Repeated keydown events are ignored, so holding a key down cannot accidentally burn through several moves in a row.
Undo does not pop a saved snapshot. Each selection adds one color letter to a visible move history, and Undo removes the latest letter and deterministically replays the remaining history from the original disclosed board. That replay model avoids hidden mutable state and makes a failed attempt repairable: undo one or more weak colors, choose a stronger sequence, and check again. Choosing the region's current color is disabled because it would not change the board and is not a meaningful move under the standard rule.
Check board runs on a clear two-strike contract. If the board is unsolved and fewer than eight moves have been made, the check reports an incomplete attempt and does not add a mistake, so you can inspect your progress freely. At eight or more moves, an unsolved board is a completed limit failure: the first failed limit check records one mistake but keeps the board and Undo active, while a second failed limit check deadlocks the run until Restart. That separates harmless early inspection from a genuinely exhausted attempt.
Scoring 1,000 Points and What That Result Means
A monochromatic board earns exactly 1,000 points only when checked at or before move eight. There is no speed bonus, no move deduction, no random modifier, and no hidden partial credit: the value is fixed, and the freeze rule is equally fixed. Once the board is solved within the limit, completion is terminal — color choices, cursor movement, undo, and repeat checks no longer change state — which prevents score farming and gives any browser-based check a stable result to read.
All rules and state transitions run locally in your browser. The game uploads no board history, requires no account, calls no remote game service, requests no device permission, and introduces no package dependency. A 1,000-point result confirms only that this one disclosed 5 by 5 fixture was finished within its proven minimum limit; it does not measure intelligence, vision, attention, or educational ability. The fixed board, the visible color-letter history, and the orthogonal-only connectivity rule together make every run fully auditable, which is the entire point of a deterministic color fill puzzle: the answer is in the rules, not in a hidden leaderboard.
For readers who want to see the same eight-move strategy worked through on a different framing, the Color Flood Puzzle: Solve a 5x5 Board in 8 Moves guide covers the same board mechanics from the solving-strategy angle.