@Pavla: I'm not certain but it may be the follwing:
Red symbolizes the Ashrafs [ie. Sharifians] of the Hijaz and the Hashemites, descendants of the Prophet
Green as their color, to symbolize their allegiance to Ali, the Prophet's cousin
White and black are certainly important colours to Muslims but I'm not sure what they mean in an Afghanistan context.
@Ana Lúcia: I'm not certain but it may be the follwing:
Red symbolizes the Ashrafs [ie. Sharifians] of the Hijaz and the Hashemites, descendants of the Prophet
Green as their color, to symbolize their allegiance to Ali, the Prophet's cousin
White and black are certainly important colours to Muslims but I'm not sure what they mean in an Afghanistan context.