Final answer:
M-8 paper turns red or reddish when exposed to an H type blister agent, which indicates the presence of chemical warfare substances such as mustard agents.
Step-by-step explanation:
When M-8 paper is exposed to an H type blister agent, it typically changes to a red or reddish color. M-8 detection paper is used to detect the presence of chemical warfare agents, specifically nerve (G series) and mustard (H series) agents. In the presence of mustard agents, which are blister agents, M-8 paper responds by turning red to indicate their presence. It is important to be aware that environmental factors and other chemicals can sometimes interfere with the accuracy of M-8 paper readings.