Why does blue 20 start Level 216?

It begins opening the cyan diamond centres and gives the first green route a bay that is already draining.

When is yellow 20 safe?

After the first blue-and-green traffic has visibly reduced; otherwise the two green 25 cards leave no working bay for yellow.

Colony Flow! level guide

hard 5 colors

Open the front blue 20, feed green traffic in the returning bays, and add yellow 20 only after the blue-diamond mosaic has room to drain.

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Tap the front blue 20 and wait for its count to fall.
Feed one green route, then the next green card while the blue ants are already moving.
Add yellow 20 only after a white bay is visibly draining.
Cycle blue 20/22 cards with green 20/25 so the diamond borders and green arches open together.
Drain the remaining yellow lane, then finish the short blue and green tails.

Colors in this level:

Blue, Green, Yellow, Cyan, White

Watch the cyan diamond centres: they should start opening before another large green card enters.
Use yellow 20 after a bay is draining, not while five bays are fresh.
Alternate later blue 20/22 cards with green cards instead of stacking duplicate greens.

Board notes 5 details

Layout: A repeating cyan-and-white diamond-flower mosaic inside dark-blue diamonds, green arches and yellow bands. Opening cards: green 25, green 25, blue 20; blue 20, yellow 20, green 20; green 20, blue 20 and blue 22, with five white bays below the hole.
Goal: Clear every cyan diamond centre, green arch, yellow band and dark-blue diamond border until the tiled panel is blank.
Opening: Start the front blue 20, let it fall, then feed green traffic before yellow 20; leave blue 22 and duplicate cards for the bays that return.
Danger Zone: Loading both green 25 cards before blue 20 drains fills the bays that yellow 20 needs and leaves the yellow arch bands waiting.
Mechanics: Three-colour perimeter routing where repeated blue diamonds, green arches and yellow bands demand a draining queue rather than a colour sweep.

Why does blue 20 start Level 216?
It begins opening the cyan diamond centres and gives the first green route a bay that is already draining.
When is yellow 20 safe?
After the first blue-and-green traffic has visibly reduced; otherwise the two green 25 cards leave no working bay for yellow.