The two colors that have always been attributed to stop signs are red and white. The likely reason for this lies within the thoughts/feelings these colors invoke, in relation to the object's intent. In this case, the stop sign intends to alert drivers to stop for oncoming traffic to ensure safety. Red is a striking, and sometimes violent color, and therefor using it as the backdrop of the sign should instantly capture the attention of any unalert driver. White is an easily seen and reflective color, and therefor an appropriate one for stop signs, which need to be visible in bad weather and at night.
Both towels (above) are of the same brand yet are different in color. The reason for this is that each person has an individual preference for color (usually dependent on their age and gender) and companies look to expand their audience by offering variety. The light red is feminine and therefor targets females, while the light green can be gender neutral. The brightness of the colors may be intentional to target a youthful audience.
