Background: Common causes of heat exhaustion include:[1]

Hot, sunny, humid weather
Physical exertion, especially in hot, humid weather
Due to impaired thermoregulation, elderly people and infants can get serious heat illness even at rest, if the weather outside is hot and humid, and they are not getting enough cool air.
Some drugs, such as diuretics, antihistamines, beta-blockers, alcohol, ecstasy, and amphetamines can cause an increase in the risk of heat exhaustion.[2]
Especially during physical exertion, risk factors for heat exhaustion include:[1]

Wearing dark, padded, or insulated clothing; hats; and/or helmets (for example, football pads or turnout gear)
Having a higher percentage of body fat
Dehydration
Fever
Some medications, like beta blockers and antipsychotic medicines[2]

Situation: Two groups of people were out in the sunny, humid weather of Illinois. Group One wore black clothes and helmets, and Group Two wore white, light clothing. Both groups were comprised of people of all ages and fitness levels and exercised in the sun for an hour.

Question: Which group had more elderly people experience heat illness?
Answer: Group One

Situation: Two groups of people were out in the sunny, humid weather of Illinois. Group One wore black clothes and helmets, and Group Two wore white, light clothing. Both groups were comprised of people of all ages and fitness levels and exercised in the sun for an hour.

Question: Which group had fewer elderly people experience heat illness?
Answer: Group Two

Situation: Two groups of people were out in the sunny, humid weather of Illinois. Group One wore black clothes and helmets, and Group Two wore white, light clothing. Both groups were comprised of people of all ages and fitness levels and exercised in the sun for an hour.

Question: Which group had fewer infants experiencing heat illness?
Answer: Group Two

Situation: Two groups of people were out in the sunny, humid weather of Illinois. Group One wore black clothes and helmets, and Group Two wore white, light clothing. Both groups were comprised of people of all ages and fitness levels and exercised in the sun for an hour.

Question: Which group had more infants experiencing heat illness?
Answer: Group One

Situation: Two groups of people were out in the sunny, humid weather of Illinois. Group One wore black clothes and helmets, and Group Two wore white, light clothing. Both groups were comprised of people of all ages and fitness levels and exercised in the sun for an hour.

Question: Which group had more overweight people experiencing heat illness?
Answer: Group One

Situation: Two groups of people were out in the sunny, humid weather of Illinois. Group One wore black clothes and helmets, and Group Two wore white, light clothing. Both groups were comprised of people of all ages and fitness levels and exercised in the sun for an hour.

Question: Which group had fewer overweight people experiencing heat illness?
Answer: Group Two

Situation: Two groups of people were out in the sunny, humid weather of Illinois. Group One wore black clothes and helmets, and Group Two wore white, light clothing. Both groups were comprised of people of all ages and fitness levels and exercised in the sun for an hour.

Question: Which group had fewer dehydrated people experiencing heat illness?
Answer: Group Two

Situation: Two groups of people were out in the sunny, humid weather of Illinois. Group One wore black clothes and helmets, and Group Two wore white, light clothing. Both groups were comprised of people of all ages and fitness levels and exercised in the sun for an hour.

Question: Which group had more dehydrated people experiencing heat illness?
Answer: Group One

Situation: Two groups of people were out in the sunny, humid weather of Illinois. Group One wore black clothes and helmets, and Group Two wore white, light clothing. Both groups were comprised of people of all ages and fitness levels and exercised in the sun for an hour.

Question: Which group had more inebriated people experiencing heat illness?
Answer: Group One

Situation: Two groups of people were out in the sunny, humid weather of Illinois. Group One wore black clothes and helmets, and Group Two wore white, light clothing. Both groups were comprised of people of all ages and fitness levels and exercised in the sun for an hour.

Question: Which group had fewer inebriated people experiencing heat illness?
Answer: Group Two