And if We send a wind, and they see it turn yellow -- behold, they then would become unthankful (disbelievers).وَلَيِنْ أَرْسَلْنَا رِيحًاAnd if We send a wind,means, a wind which dries up the crops which they have tended and cultivated and which have matured, and they see them turn yellow, and start to rot, if this were to happen, they would become ungrateful, i.e., they would deny the previous blessings that they were given.This is like the Ayah,أَفَرَءَيْتُم مَّا تَحْرُثُونَThen tell Me about the seed that you sow in the ground. until:بَلْ نَحْنُ مَحْرُومُونَNay, but we are deprived! (56:63-67