The Mekhilta DeRabbi Yishmael drew a sharp distinction between two foods God gave the Israelites in the wilderness, and the difference had everything to do with how they were requested. The quail and the manna both came from heaven, but they arrived under very different circumstances.
The quail was requested "with a full stomach." The Israelites were not truly starving when they demanded meat. They had food. They had the manna. But they wanted more, wanted variety, wanted the fleshpots they remembered from Egypt. Because the request came from excess rather than genuine need, God gave them the quail with a "darkened countenance," meaning grudgingly, with displeasure.
The manna, by contrast, was requested legitimately. When the Israelites first cried out for bread in the wilderness (Exodus 16:3), they were genuinely hungry. They had nothing to eat. Their need was real and desperate. Because the request arose from true hunger, God gave the manna with a "radiant countenance," meaning generously, with joy and openness.
Moses and Aaron then turned the lesson back on the people. "Of what significance are we that you stand and rail against us?" they asked. The Israelites' complaints were directed at Moses and Aaron, but Moses pointed out that their real grievance was with God Himself. He was the one who decided what to give and how to give it. Moses and Aaron were merely messengers. The distinction between darkened and radiant countenance was God's judgment, not theirs.