Which groundbreaking 20th century invention was deliberately colored bright yellow to create brand recognition, despite the color having no functional purpose for the product?

Throughout the history of inventions and discoveries, innovators have used design psychology to enhance product appeal. Color choices in particular have played a fascinating role in how revolutionary inventions were marketed and perceived by the public. This trivia challenge explores a notable case of deliberate color selection that transformed an invention's market presence and created lasting brand recognition in the scientific community.

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Post-it Notes
Polaroid Instant Camera
Walkman Portable Cassette Player
IBM Personal Computer