When should the white vertical receiver move?

Move it only after the yellow shutter has dropped and the central counter has begun falling; otherwise it blocks the red feed.

What is the late-board reserve?

Keep the broad lower cells empty for the final horizontal cyan and purple receivers.

Sand Blocks level guide

expert 7 colors

Level 288 spends the yellow 2-shutter, walks the red feed through a 14-counter center, and holds the bottom row for cyan and purple 2x2.

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Place cyan 1x2 at r1c1-r1c2 and cyan 1x3 at r1c4-r1c6; fit green corner at r2c1-r3c2 and yellow corner at r2c5-r3c6. Leave shaft c3 open.
Let yellow reduce the top shutter 2 to 1, then slide white vertical from c3,r4-r6 to c2,r4-r6 so central 14 is exposed.
Route red through c3, alternating cyan horizontal r5c3-r5c5 with purple bar r6c3-r6c5; confirm 14→12→10 after each pair.
Move yellow 1x2 to r4c1-r4c2 and green corner to r4c5-r5c6; reserve r7-r8,c5-c6 for purple.
At counter 4, 3, then 2, place white gate at c1,r5-r7 and cyan vertical at c6,r5-r7; keep the right outlet open.
When feed turns purple and counter reaches 1, place cyan horizontal at r8c2-r8c4 and wait for its 100% fill.
Drop purple 2x2 into r7-r8,c5-c6, then wait for the 1-counter transition and empty board.

Colors in this level:

Yellow, Cyan, Green, Purple, Red, White, Pink

Filling the central shaft with the white bar before the red feed begins.
Parking a yellow bar in the lower-right pocket before the purple landing is exposed.
Sealing the right outlet while the counter is still above 1.

Board notes 5 details

Layout: Yellow top tube feeds a shutter marked 2; cyan shelf pieces sit above a central 14 counter, with green, purple, yellow, cyan, white, and pink receivers below.
Goal: Lower the yellow shutter, drain the red feed through the central shaft, and preserve lower-grid cells for the final cyan and purple receivers.
Opening: Catch cyan shelf pieces and place green/yellow corners at side pockets; keep the shaft open before moving the white vertical bar.
Danger Zone: The white bar in the central shaft traps the red layer if moved too early; a yellow bar in the lower-right pocket blocks the final purple horizontal landing.
Mechanics: Yellow-to-red-to-purple staged feed, repeated counter changes from 14 toward 1, and a large white vertical gate are evidenced.

When should the white vertical receiver move?
Move it only after the yellow shutter has dropped and the central counter has begun falling; otherwise it blocks the red feed.
What is the late-board reserve?
Keep the broad lower cells empty for the final horizontal cyan and purple receivers.