What type of spray can be applied to an envelope to enhance visibility of the contents?

The correct choice in this context is reflective spray. This type of spray is designed to enhance the visibility of an item by reflecting light, which makes it easier to see the contents of an envelope in various lighting conditions. Reflective materials can be particularly useful in situations where visibility is crucial, such as in low-light environments or during emergencies where quick identification of contents is necessary.

Transparency spray typically refers to a spray that may enhance clarity or gloss but does not enhance visibility in the same manner as reflective materials. Marker spray often refers to a color-based spray that marks surfaces but does not serve the purpose of improving visibility through reflection. Color change spray may alter the color of a surface but does not inherently enhance visibility as reflective spray does.