The mood of Ceremony is grim, given the heavy traumas Tayo experiences both in wartime and as an Indian American. Notably, this grim mood improves as Tayo goes through the "ceremony," eventually refusing to continue the cycle of violence he finds himself in.
In opposition to this heavy, dark mood is one of hope, reverence, and reflection, often triggered by Tayo's proximity to nature and love for its creatures. Note the following passage from Section 3:
When the shadows were gone, and the cliff rock began to get warm, the frogs came out from their sleeping places in small cracks and niches in the cliff above the pool. They were the color of the moss near the spring, and their backs were spotted the color of wet sand. [....] They swam across the pool to the sunny edge and sat there looking at him, snapping at the tiny insects that swarmed in the shade and grass around the pool. He smiled. They were the rain’s children.
This passage is almost meditative in nature, with Tayo taking the time to reflect on his love for the small frog, as yet another of "rain's children." When Tayo looks outside himself, considering his place in the ecosystem around him and his existence in harmony with the land, connected to all of its creatures, he regains his hope—even if the strength of said natural relationships emerges in flashback.