Refer to figure. 
POSITIVE G-FORCES

When experiencing high positive g-forces, the body undergoes increased gravitational stress, which can force blood to pool in the lower part of the body. This reduces the blood supply to the brain and the eyes. Reduced blood Flow to the eyes can cause:

• Grey out: With less blood reaching the eyes, the retina receives less oxygen and nutrients, leading to a temporary loss of vision that starts with peripheral vision and can progress towards the center, resulting in a "grey-out" effect where vision fades to grey.
• Black out: A condition where an individual experiences a total loss of vision and consciousness due to insufficient blood and oxygen supply to the brain, often resulting from high positive g-forces. During a blackout, the gravitational forces pull blood away from the brain, leading to a temporary shutdown of brain function and visual perception.

Positive g-forces → grey out and eventually black out 
Negative g-forces → red out

Let's examine the given options:

Vertigo → INCORRECT. Vertigo is a sensation that you or your surroundings are spinning or moving, even though there is no actual movement.

Red-out → INCORRECT. It occurs during negative “g” forces, when blood is pulled downward away from the brain and eyes and vision appears redish due to the blood.

Grey-out → CORRECT. With less blood reaching the eyes, vision fades to grey during positive “g” accelerations.

Hyperventilation → When a pilot experiences strong positive g-forces, blood is pulled away from the brain toward the lower body. This reduces the amount of oxygen-rich blood reaching the brain, creating a situation similar to hypoxia (lack of oxygen), not hyperventilation.