The discussion centers around the phenomenon of double rainbows, sparked by a user sharing a picture of one. It explains that double rainbows occur due to light reflecting twice within raindrops, creating a primary rainbow and a fainter secondary rainbow with reversed colors. The primary rainbow has red on the outside, while the secondary has red on the inside. This optical effect is common but often faint, making it less frequently observed. The conversation also touches on the visual beauty of rainbows and personal experiences of observing them, emphasizing the joy and wonder they inspire. Additionally, links to further resources and lectures on the topic are shared for those interested in a deeper understanding of the science behind rainbows.