What do the four colors "red, blue, yellow and green" mean?

Red means: no, stop, which also means fire prevention; Blue indicates: instructions or regulations that must be observed; Yellow means: warning, attention; Green means: indication, safety status and traffic.

Safety colors are widely used, such as safety signs, traffic signs, protective railings and machine parts that are not allowed to move.

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Use:

The International Organization for Standardization (ISO) and many countries have strict regulations on the use of safety colors. China has formulated the national standard of safety color. Red, yellow, blue and green are specified as national security colors. The meanings and uses of the four safety colors are as follows:

red

It means prohibition, stop, fire fighting and danger. Prohibited, stopped and dangerous devices, equipment or environment are marked in red. For example, prohibition signs, traffic prohibition signs, fire-fighting equipment, stop buttons and operating handles of parking and braking devices, limit position scales on instrument panels, exposed parts of rotating parts of machines, strips and characters of liquefied petroleum gas tankers and danger signal signs.

yellow

It means to pay attention and warn. Devices, equipment or environments that need to be warned are marked in yellow. Such as warning signs, traffic warning signs, road traffic signs, inner walls of pulleys and their protective covers, inner walls of grinding machine covers, front steps of the first and last steps of stairs, protective railings and warning signal signs.

blue

Indicates the instructions and rules that must be followed. Such as indicator signs, traffic signs, etc.

green

It means transportation, safety and providing information. Traffic or safety conditions can be marked in green. For example, it indicates traffic, machine start button, safety signal sign, etc.

Black and white are generally used as the contrast colors of safety colors, mainly used as the background color of the above safety colors. For example, the background color on safety signs is usually white or black.

References:

Baidu Encyclopedia-Safety Color