The Giver tries to show Jonas pleasurable memories after sharing pain with him. He shows him yellow wildflowers and yellow smoke.
As Jonas’s training continues, he faces difficult memories. Sometimes he is in unbearable pain. However, The Giver tries to end on a high note.
Each time, in his kindness, The Giver ended the afternoon with a color-filled memory of pleasure: a brisk sail on a blue-green lake; a meadow dotted with yellow wildflowers; an orange sunset behind mountains. (ch 14, p. 110)
These are positive associations Jonas has with color. There is no color in the community, because of Sameness. Jonas first new he was different when he started seeing the color red. As a result, he likes seeing color.
Jonas also experiences negative memories with color, such as war. He sees the color yellow, this time associated with pollution.
He was in a confused, noisy, foul-smelling place. It was daylight, early morning, and the air was thick with smoke that hung, yellow and brown, above the ground. (ch 15, p. 118)
Jonas also is shocked by the yellow of the boy’s hair as he begs for water, dying on the field. The contrast of his hair and the green grass is startling and sad. Jonas finds the memory hard to get over, and later tries to stop Asher from playing a war game.
Jonas is getting a complete education through the memories. He is seeing everything vividly- both good and bad. The color helps him have the full experience.
Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book). Houghton Mifflin Harcourt. Kindle Edition.