The Environment rollout specifies colors or texture maps to be used during GI and reflection/refraction calculations. If a color/map is not specified, the background color specified in the Environment rollout of the current camera is used.

UI Path: ||Render Settings window|| > Overrides tab > Environment rollout

Override Environment – When enabled, V-Ray overrides the default Maya environment and renders with the options selected below. Many options on this rollout appear only after this option is enabled.

Override Secondary Matte Environment – When enabled, V-Ray overrides the reflection/refraction environment for matte objects.

Background texture – Sets a color or a map to act as a background during rendering. Press the checkerboard button to select a texture. If a texture is selected, it will override the selected color.

GI texture – Sets a color or a map to be used during Indirect Illumination(GI) calculation. The effect of changing the GI texture is similar to skylight. Press the checkerboard button to select a texture. If a texture is selected, it will override the selected color.

Reflection texture – Sets a color or a texture to be used during calculations of reflections. Press the checkerboard button to select a texture. If a texture is selected, it will override the selected color. Starting with V-Ray 3.6, environment reflections can be previewed in V-Ray Material (VRayMtl) reflections with Viewport 2.0.

Refraction texture – Sets a color or a texture to be used during calculations of refractions. Press the checkerboard button to select a texture. If a texture is selected, it will override the selected color.

Secondary Matte texture – Sets a color or a texture to be used during calculations of reflections/refractions of matte objects. This option is available only when Override Secondary Matte Environment is enabled.

Show in viewport – When enabled, Maya displays one of the textures used to override the environment.

Use texture for – Sets exactly which texture will be displayed for the following options:

Background 
GI 
Reflection 
Refraction 
Secondary Matte

Options – Creates and/or selects the VRayEnvironmentPreview node, which allows more control over the viewport texture.

Create Sun – Creates a V-Ray Sun object in the scene. For more information, please see the V-Ray Sun and Sky System page under V-Ray Lights in this documentation.

Delete Sun – Deletes the V-Ray Sun object currently in the scene.

Create Sky – Creates a V-Ray Sky object in the scene. For more information, please see the V-Ray Sky Map page under V-Ray Textures   in this documentation.

Delete Sky – Deletes the V-Ray Sky object currently in the scene.