Yes, there are shades of gray from dark to light, but they're called great gray for a reason, size and color. To see them fly, the first thing that impresses you is their wing size with their long, broad graceful sail-like wings catching air underneath their plumes. Their nesting biology is rather straight forward for an owl. The Great Gray Owl does not make its own nest, but rather uses abandoned nests of other raptors especially of the Northern Goshawk. They typically make their nests atop broken snags as well.
Owls have a specific nesting biology with their own terms.
When the chicks are born, they are called nestlings. At about four weeks old, the nestlings still covered with down and a hint of emerging feathers, leave the nest in a controlled crash to the ground. They then become what is called branchlings. The young scurry about the ground, along downed trees and walk up branches to get fed which is where the term branchling comes from. They stay around the nest area during this time.