Then Moses and Aaron, Nadab, and Abihu, and seventy of the elders of Israel went up, and they saw the God of Israel. There was under his feet as it were a pavement of sapphire stone, like the very heaven for clearness.
#exodus 24:9-10 #mishpatim

The sky is blue to remind us of the floor of God's throne room, which is also the reason for the blue thread in the tzitziyot. God's floor is transparent. He's watching us.