Which stack should I lead with in Colony Flow Level 21?

Lead with the gray 25 cube in slot 1 of the 5-cell top buffer row first. It is the only cube pre-loaded in the active row, and clearing it frees the slot for the rising green 25 to land cleanly in slot 2 and start the green frame. Then run the green 25 / green 22 / green 20 trio as one continuous wave, send the black 20 / black 18 / black 20 trio for the deep-purple body, dispatch the x1 ant in the middle of row 3 to unlock the gray row, and finish with the gray 20 and gray 22 plus the late gray refill waves to close the inner band.

Why does the route jam if I switch colors too early in Colony Flow Level 21?

The two gray 20 and gray 22 cubes on row 3 of the supply grid are locked behind the x1 ant icon in the middle of row 3, and they cannot rise into the active buffer row until the x1 ant is dispatched. If the player taps the gray 20 or gray 22 directly without first dispatching the x1 ant, those gray cubes stay in the supply grid, the gray/silver inner band between the dark body and the green frame stays half-open, and the three white highlight cells in the body never get exposed cleanly.

Colony Flow! level guide

Colony Flow! Level 21 Walkthrough

medium 3 colors

Colony Flow Level 21 is a tight 5-cell-buffer / 3x3-supply-grid board where the pixel-art target is a rounded dark-purple jelly-bean / grape shape with three white highlight cells inside the dark body and a solid green background frame around it.

Board Notes

Layout: The board opens in portrait view. The top half of the screen holds a pixel-art jelly-bean / grape silhouette: a rounded, slightly tilted deep-purple body with three small white highlight cells punched into the body, wrapped in a thin gray/silver inner band, and set against a solid green background frame. A single dark round ant hole sits on a dirt strip directly below the pixel art, with one small ant already climbing up the trail. Below the dirt strip, the working area is an L-shaped 5-cell top buffer row sitting above a 3-cell-wide, 3-row main supply grid. The 5-cell buffer row opens with the gray 25 cube pre-loaded in slot 1 and four empty white buffer pads in slots 2-5. The 3x3 supply grid reads, top to bottom and left to right: black 20 / black 18 / black 20 on row 1, green 25 / green 22 / green 20 on row 2, and gray 20 / x1 ant icon / gray 22 on row 3., all showing +0.
Goal: The three green 25 / 22 / 20 stacks on row 2 of the supply grid must fill the solid green background frame around the jelly-bean. The three black 20 / 18 / 20 stacks on row 1 of the supply grid must fill the deep-purple body of the jelly-bean itself and expose the three white highlight cells inside. The gray 25 cube pre-loaded in buffer slot 1, the gray 20 and gray 22 on row 3 of the supply grid, and the late gray refill waves must fill the thin gray/silver inner band between the dark body and the green frame. The x1 ant icon in the middle of row 3 is a one-shot dispatch that unlocks the gray row, and it has to be tapped before the gray 20 or gray 22 can rise into the active buffer row.
Opening: The first confirmed tap is the gray 25 cube in slot 1 of the 5-cell top buffer row. It is the only cube already in the active row at start, and clearing it is what frees the slot so the green 25 (which rises into slot 2 as a partly-consumed 11-cube green stack) can start closing the green frame. The second confirmed tap is that 11-cube green stack in buffer slot 2, which dispatches the first green ants up the dirt path to start filling the green background frame. The third confirmed tap is the green 22 stack on row 2 of the supply grid, followed by the green 20 on row 2, so the three green stacks run as one continuous wave and the green frame closes in a single beat. The black 20 / 18 / 20 on row 1 of the supply grid are held for one beat so the green frame can be at least half-drawn before any black ant enters the trail.
Danger Zone: The danger zone is the x1 ant icon in the middle cell of row 3 of the supply grid. The two gray 20 and gray 22 cubes on either side of the x1 ant cannot rise into the active buffer row until the x1 ant has been dispatched, and tapping the gray 20 or gray 22 directly before the x1 ant goes leaves the gray row stranded and the gray/silver inner band of the jelly-bean never closes. The other trap is firing the black 20 / black 18 / black 20 on row 1 of the supply grid before the green 25 / 22 / 20 wave has at least half-closed the green frame, because black and green ants use the same dirt path and a premature black click dumps black ants into the still-empty body cells and stalls the next green refill behind them. Tapping the green 25 twice in a row is also bad, because the green frame cells are smaller than the body cells and a double-tap floods the dirt strip with green ants that have nowhere clean to land.
Mechanics: Level 21 is a single-color opener board (the gray 25 in buffer slot 1) layered on top of a multi-stack color-routing board (the 3x3 supply grid) with a pixel-art completion goal and a single ant hole. The L-shaped 5-cell buffer row plus 3-cell-wide 3-row supply grid is a tighter variant of the L-shaped layout used in Levels 18 and 19, but with only eight numbered cubes plus one x1 ant compared with the wider 4x4 grids. The pre-loaded gray 25 in buffer slot 1 is the unusual mechanic, since most boards open with an all-empty buffer, and that single gray 25 has to be cleared first or it locks the gray row behind it. The x1 ant in the middle of row 3 is the other unique mechanic, since it acts as a one-shot unlocker for the gray stacks and only appears on a small subset of Colony Flow! boards. so the last single-digit gray refill waves and the final x1 ant dispatch still need a clean delivery after the bottom of the grid looks clear.

Quick Tips for Colony Flow! Level 21 (spoiler-free)

Tap the gray 25 in slot 1 of the 5-cell top buffer row first. It is the only cube pre-loaded in the active row, and clearing it is what frees the slot for the rising green 25 to land cleanly in slot 2 and start the green frame.
Run the green 25 / green 22 / green 20 trio on row 2 of the supply grid as one continuous wave before any black ant enters the trail. The green frame is the outermost region of the jelly-bean and has to be at least half-drawn before the deep-purple body starts absorbing black ants.
Dispatch the x1 ant in the middle of row 3 of the supply grid before you tap the gray 20 or gray 22 next to it. The x1 ant is the only thing that unlocks the gray row on this board, and a gray 20 click before the x1 ant dispatch strands the gray 22 and leaves the gray/silver inner band half-open for the rest of the run.

How to Solve Colony Flow! Level 21 — Full Solution

Tap the gray 25 cube in slot 1 of the 5-cell top buffer row. Gray ants walk the dirt strip up to the thin gray/silver inner band of the jelly-bean and slot 1 opens up for the next refill. Wait for the first gray ants to clear the bottom edge of the art before tapping the next stack.
Tap the green 11 stack that has risen into buffer slot 2 (it is the green 25 from row 2 of the supply grid, partly consumed). Green ants walk the same dirt path and start filling the green background frame around the jelly-bean. The green frame cells are smaller than the body cells, so leave one beat before tapping the next green.
Tap the green 22 stack on row 2 of the supply grid, then the green 20 stack on row 2. Run the entire green 25 / green 22 / green 20 trio as one continuous wave so the green frame closes in a single beat. Do not double-tap the green 25 or the dirt strip floods with green ants that have no clean landing cell.
Tap the black 20 stack on the left of row 1 of the supply grid, then the black 18 in the middle, then the black 20 on the right. Black ants walk the dirt path and start filling the deep-purple body of the jelly-bean. The black trio goes after the green frame is at least half-drawn so the body cells behind the frame are open.
Dispatch the x1 ant icon in the middle cell of row 3 of the supply grid. This is the one-shot unlocker that lets the gray 20 and gray 22 cubes flanking it rise into the active buffer row. Without the x1 ant, the gray row is stranded and the gray/silver inner band never closes.
Tap the gray 20 stack on the left of row 3, then the gray 22 stack on the right of row 3, as soon as they rise into the active buffer row. Gray ants walk the dirt path and start closing the thin gray/silver inner band between the dark body and the green frame.
Drain any small gray or green refill waves (single-digit cubes) that climb up from the supply grid during the run. Each refill tap should be a single-tap beat so the late ants can find clean landing cells around the three white highlight cells.
Finish by waiting for the very last ant to return to the ant hole. The jelly-bean silhouette is fully colored, the three white highlight cells are exposed inside the dark body, the green frame is closed, the gray/silver inner band is closed, and the level banner appears.

Colors in this level:

Gray, Green, Black

Common Mistakes to Avoid

Tapping the gray 20 or gray 22 on row 3 of the supply grid before dispatching the x1 ant icon in the middle of row 3, which strands the gray row and leaves the gray/silver inner band of the jelly-bean half-open for the rest of the run.
Firing the black 20 / black 18 / black 20 trio on row 1 of the supply grid before the green 25 / green 22 / green 20 wave has at least half-closed the green frame, which dumps black ants into still-empty body cells and stalls the next green refill behind them on the dirt path.
Double-tapping the green 25 from row 2 of the supply grid back to back, which floods the dirt strip with green ants that have no clean landing cell and strands the late gray refill waves behind the green jam.

Frequently Asked Questions

Which stack should I lead with in Colony Flow Level 21?
Lead with the gray 25 cube in slot 1 of the 5-cell top buffer row first. It is the only cube pre-loaded in the active row, and clearing it frees the slot for the rising green 25 to land cleanly in slot 2 and start the green frame. Then run the green 25 / green 22 / green 20 trio as one continuous wave, send the black 20 / black 18 / black 20 trio for the deep-purple body, dispatch the x1 ant in the middle of row 3 to unlock the gray row, and finish with the gray 20 and gray 22 plus the late gray refill waves to close the inner band.
Why does the route jam if I switch colors too early in Colony Flow Level 21?
The two gray 20 and gray 22 cubes on row 3 of the supply grid are locked behind the x1 ant icon in the middle of row 3, and they cannot rise into the active buffer row until the x1 ant is dispatched. If the player taps the gray 20 or gray 22 directly without first dispatching the x1 ant, those gray cubes stay in the supply grid, the gray/silver inner band between the dark body and the green frame stays half-open, and the three white highlight cells in the body never get exposed cleanly.