Which safety colors are not present in mandatory instruction signs?

Mandatory instruction signs are designed to convey essential instructions that pilots must follow while on the ground, such as “Do not enter” or “Stop.” These signs typically use a specific color scheme to ensure that their messages are clear and easily recognizable.

The color red is prominently used in mandatory instruction signs to communicate prohibitions, such as "no entry" or "stop." White is often used as a background color. Therefore, the combination of red and white is standard for these signs.

The options yellow and black, or blue and white, do not necessarily pertain to mandatory instruction signs. Yellow and black are typically associated with cautionary signs (like warning signs), which indicate potential hazards rather than mandatory instructions. Blue and white are generally used for information signs, indicating service and facilities, rather than mandatory instructions.

Red and green, while green is used for movement area signs (indicating safe areas), do not apply to mandatory instruction signs, as the primary purpose of green is not to indicate either mandatory or prohibited actions.

Thus, the option indicating the absence of red and green aligns correctly with the characteristics of mandatory instruction signs, reinforcing their distinct color usage and indicating which colors do not fit within this sign category.