Bright and bold colours are used on bollards because they provide an extra measure of safety for a variety of different uses.
For example, pedestrian areas near high-traffic zones increase the risk of danger to anyone walking past. Bright coloured bollards such as red or yellow that clearly separate the street from the pavement tell drivers to stay clear and in their lanes.
In addition, bold and bright coloured bollards stand out more in dimly lit areas which is invaluable. For example, warehouse workers on late night shifts operating heavy pieces of machinery can pose a danger risk if bright road bollards are not in place to guide and highlight designated areas.
Since brightly coloured road bollards are more visible in the dark, they can assist the direction of traffic if there ever was a local power outage.