枪口位河牌圈最小加注彩虹面（UTG River Min-Raise Rainbow）
Refers to a specific situation where the player in the UTG under the gun position makes a minimum raise on the river, and the community cards have all different suits i.e., a rainbow board.
Position and Stage
UTG (Under the Gun) is the first to act preflop, but position is fixed postflop. The river is the betting round after the fifth community card is dealt, when all five community cards are visible.
Action: Min-Raise
A min-raise refers to a raise that is exactly equal to the current maximum bet (or raise) amount, typically double the previous player's bet. On the river, a min-raise is often used as a probe or value extraction, but it may also reveal hand strength.
Board Texture: Rainbow
A rainbow board means all five community cards are of different suits (i.e., one heart, one spade, one club, one diamond, and the fifth card is any suit but different from the first four). This feature eliminates any possibility of a flush draw or made flush, so hand strength evaluation relies more on single card strength or straights.
Strategic Implications
In this scenario, an UTG player min-raising on the river typically indicates holding the nuts or a very strong made hand, aiming to extract value from an opponent's weaker made hands or bluffs while avoiding a fold. Since the rainbow board lacks flush possibilities, the opponent's drawing range is narrowed, making UTG's raise more likely to represent a made strong hand. This action may also be used against aggressive opponents' thin value bets or bluffs.