All green 緑一色 · ryuuiisou

Short answer: Ryuuiisou (all green) is a yakuman, open or closed, for a hand made only of green tiles: bamboo 2, 3, 4, 6, and 8, plus the green dragon.

Every tile is green: bamboo 2, 3, 4, 6, 8 and the green dragon only.

Value	Yakuman
How often	very rare

Mahjong hand: 2 of bamboo, 3 of bamboo, 4 of bamboo — 2 of bamboo, 3 of bamboo, 4 of bamboo — 6 of bamboo, 6 of bamboo, 6 of bamboo — 8 of bamboo, 8 of bamboo, 8 of bamboo — green dragon, green dragon — Only green tiles: 2, 3, 4, 6, 8 of bamboo and the green dragon.

You rarely plan ryuuiisou from the deal. It usually reveals itself a few turns in, when a bamboo-heavy hand headed for a half flush turns out to be using only the green tiles: bamboo 2, 3, 4, 6, and 8, plus the green dragon, hatsu 發. Since 2-3-4 is the one sequence those numbers allow, every other set must be a triplet, so the hand leans on 234 runs and pons of 6s, 8s, and the dragon.

It counts open or closed, so call freely once you commit. The chase is also cheaper than it looks, because a failed attempt usually still lands as honitsu or a full flush. The classic mistake is treating every bamboo tile as green: 1, 5, 7, and 9 of bamboo all carry red in their design and disqualify the hand. One more check before you chase a version with no dragon at all — some tables require the green dragon, so confirm the table's rule first.

Key points

The one yakuman defined by tile color rather than structure
Whether the green dragon is required varies by ruleset — pure-bamboo versions are debated
Said to have been popularized by American players before returning to Japan

Worked example

Mahjong hand: green dragon, green dragon, green dragon — 2 of bamboo, 3 of bamboo, 4 of bamboo — 2 of bamboo, 3 of bamboo, 4 of bamboo — 4 of bamboo, 4 of bamboo — 8 of bamboo, 8 of bamboo, winning tile: 8 of bamboo — An open all-green hand: a called triplet of Green dragons, two 234s runs, a 44s pair, and an 88s pair. All four 4s are already in the hand, so the green winning tile is the 8s.

You pon the Green dragons early and keep only green tiles after that. At tenpai the hand holds 234s twice, a pair of 4s and a pair of 8s. Win on the 8s and every tile is green: ryuuiisou, a yakuman — 32,000 for a non-dealer even though the hand is open. Because the green dragon is in it, the hand qualifies under both versions of the rule.

Now the trap: this hand also completes on a 1s, reading as 123s, 234s, and 444s. The 1s is not green, so that win is not ryuuiisou — it drops to an open honitsu plus the dragon yakuhai. Before you call ron, check the tile, not just the shape.

Common mistakes

Treating every bamboo tile as green. The 1, 5, 7, and 9 of bamboo all carry red and disqualify the hand.
Assuming the green dragon is optional everywhere. Some tables require it; others accept all-bamboo green hands. Ask first.
Forgetting that 234 is the only green sequence. Everything else must be a triplet or the pair.

Rule variations

Some rules require the green dragon; others allow all-bamboo green hands. Check the table's ruleset.

Related yaku

Full flush 清一色 — The entire hand is one suit — the highest-value regular yaku in the game.
All honors 字一色 — The whole hand is honor tiles — winds and dragons only.

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