Which NATO marker color indicates a hazard from biological contamination?

The marker color that indicates a hazard from biological contamination is indeed white with black letters. NATO uses a specific color-coding system to communicate various hazards clearly, and in this context, the white background with black lettering serves to alert personnel to the presence of biological hazards. This visibility is crucial in quickly conveying an important message about potential dangers, ensuring that those in the area can take appropriate action to protect themselves from biological threats.

The other options represent different hazards: red typically indicates fire hazards, blue is often used for safety information or administrative instructions, and purple with yellow letters represents hazards related to radiation. Understanding this color-coding system is vital for ensuring safety and effective communication in operations involving NATO forces.