Environment
From ZBrush Info
The Environment subpalette allows you to globally reflect a single image or color on all the objects in the scene with reflective surfaces. The amount of environmental reflection is set in the Material palette for each material.
Controls
Off: Turns off Color, Texture, or Scene reflections. Default = pressed (environmental reflections off).
Color: When on, lets you use a single color for global reflections. Pressing the Color button enables the Environment Color patch.
Txtr: Allows a texture to be used for global reflections. Pressing the Texture button enables the Environment Texture patch.
Scene: When on, uses the current scene as a source image for global reflections.
Environment Color (in the figure above, the blue square): When the Color switch is on, use this patch to selecte the environment color. Select a color with any of the color pickers and click on Environment Color, or click and drag from Environment Color to any part of the canvas or interface to pick a color.
Environment Texture (in the figure above, the small square showing a scene): When Txtr is on, click and hold on the Environment Texture patch to access the texture sub-palette and choose a texture.
Trace Distance: The trace distance is how far ZBrush will look to find a local object to reflect. Range = 0 to 100% of the current image size. Default = 50%.
Repeat: Controls how many times a reflective surface can reflect another reflective surface. The effect can be visualized by facing two mirrors at each other. Range = 1 to 5. Default = 1.
Field of View: Sets the field of view for environmental mapping and lights. A setting of zero degrees causes the point of view to be infinitely far away. A setting of 180 degrees places the point of view right above the canvas. Range = 0 to 180 degrees. Default = 0.
Field of View = 0 
Field of View = 120 
Field of View = 180 
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