Red, white, black and green were the colors of the Arab Revolt flag which Kuwait and some other Arab nations used in the revolt of the Arab nations against the Ottoman Empire (Turkey) during WWI.
The flag was a red triangle with its base on the hoist (left side of the flag. It had three horizontal stripes of equal sizes of black, green and white.
The colors on this flag were chosen to honor three Caliphates and one dynasty. Black for Abbusid, green for Umayyad, white for Falmid and red for the Hashemite dynasty, all of which were allies of the British during the war.
The current flag of Kuwait was adopted on 7 September 1961 when they gained independence from Britain. It was first hoisted on 24 November 1961.
The flag was replaced when Iraq invaded in August of 1900 and restored when Kuwait was liberated in February 1991 with help from American troops.
The flag of Kuwait now in use has a black trapezoid at the hoist and three horizontal equal stripes of green representing fertile fields. The white is for honor and purity, red blood of defeated enemies and black represents the defeat of enemies.
Another set of meanings is that white signifies honor, red is for gallantry, bravery, strength and valor, green represents fertile fields, hope, joy, love and in many cultures green has a sacred meaning, and black is for the defeat of enemies or determination.
These colors appear on many flags. Yet another set of meanings is white: deeds, black: battlefields, green: meadows, red: blood of enemies. One more set, white: honor, black: sand whirled by Kuwaiti horsemen, green: fields, red: gallantry.