The discussion centers around a common misconception that blood is blue, particularly focusing on the belief that deoxygenated blood appears blue. Participants provide various explanations to clarify that blood is red in both its oxygenated and deoxygenated states, although the shades differ. Key points include the role of hemoglobin, which cannot be blue without significant chemical changes, and the visual perception of veins, which may appear blue through the skin. Suggestions for convincing the brother include showing him blood directly, such as through a blood donation, to illustrate its true color. The conversation also touches on the origins of the misconception, possibly stemming from biology education, and emphasizes the importance of understanding the chemistry behind blood color. Overall, the consensus is that blood is red, and the misconception is largely based on misunderstanding and visual perception.