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Based on – Specifies the source channel used to determine the smoke color. By default, a uniform simple color set by the the Constant Color option is used. This could also be a texture map, or read from the cache files - in that case the corresponding grid channel must be present in the cache files and remapped to the internal Volume Grid channels using the 3rd Party Channels Mapping dialog in the Input roll-out.

Disabled - Smoke color is not rendered.
Temperature - Smoke color is based on the values of the Temperature cache channel and can be remapped using the color gradient.
Smoke - Smoke color is based on the values of the Smoke cache channel and can be remapped using the color gradient.
Speed - Smoke color is based on the values of the Speed cache channel and can be remapped using the color gradient. See the Smoke Color by Speed example below.
Texture - Smoke color is based on the values of a texture map plugged into the Texture slot.
Constant Color - Smoke color is the same for the entire volume and is taken from the Constant Color box.
RGB - Smoke is based on the values of the RGB channel.
Fuel - Smoke is based on the values of the Fuel channel and can be remapped using the color gradient.

Smoke Color Texture – If Based on is set to Texture, this slot specifies which texture to use.

Modulate by Texture – When Based on is not set to Texture, the color is multiplied by the texture in the Texture slot.

Constant Color – If Based on is set to Constant color, this color is used. 

Scattering – Controls how the light rays are scattered inside the volume.

Ray-traced (GI only) – Enables physically accurate scattering of light rays. This mode produces the most realistic results but it's the slowest to render. It requires V-Ray with enabled Global Illumination, otherwise, the rendered result would be the same as if the option is Disabled. The Master Multiplier does not affect the rendering in this mode.
Disabled – Disables scattering. The Master Multiplier value can be used to correct the brightness because without light scattering the volume would generally render darker.
Approximate – Uses an approximate formula which is faster than Ray-Traced scattering and produces good-looking results. Brighter areas of the volume would transfer light farther than dark areas. This option is not supported by the Volumetric Geometry render mode in the Rendering tab.
Approximate+Shadows – Same as Approximate, but also affects the strength of shadows over the scene geometry. Approximate+Shadows is not supported by the Volumetric Geometry render mode in the Rendering tab.

Phase Function – Controls the direction in which the light scatters inside the volume. Negative values correspond to backward scattering, which mimics a volume made up of solid particles and produces denser and more detailed looks. Negative values are more suitable for smoke or dust effects. Positive values correspond to forward scattering, which mimics a volume made up of water droplets where light scatters more. Positive values are suitable for highly scattering volumes such as clouds. The default value of 0 scatters the light in all directions and creates an even and diffuse look. See the Phase Function examples for a visual representation.
Note that values very close to 1.0 or -1.0 produce very directional scattering that is invisible from most angles, so such values are not recommended. When rendering with a Phase Function different than 0 and Volume Light Cache is enabled, the rendered result is brighter. The Phase function is ignored when the scattering is set to Approximate or Approximate+Shadows.

Optimize Anisotropic Scattering – When enabled, it can greatly reduce the render times for highly scattering volumes such as clouds. Due to certain assumptions made for the optimizations, the optimized render result might produce different results compared to the exact brute-force anisotropic scattering. The option is ignored when the scattering is set to Approximate or Approximate+Shadows.

Scatter Depth – Specifies the maximum depth of the GI rays.

Volume Light Cache – Enables light caching for each voxel of the grid, which speeds up bucket rendering considerably when the voxel size of the grid is significantly larger than the rendering pixel. If the grid resolution is large enough compared to the rendering resolution, disabling this option speeds up rendering.

Light Cache Speedup – Valid only when Volume Light Cache is enabled. The higher this option is set, the faster the rendering will be, but the lower the quality of the volumetric Light Cache. You can increase this parameter and gain render speed as long as you don't start getting dark cubic grid artifacts on the smoke.

Own Light Scatter Mult – Valid only when Scattering is set to Approximate or Approximate+Shadows. This multiplier determines how far the light travels through the volumetric, based on the distance from the emissive light itself.

External Scatter Mult – Valid only when Scattering is set to Approximate or Approximate+Shadows. This multiplier determines how far the light from all external light sources travels through the volumetric. Both Scatter Boost parameters don't alter the visual density of the smoke to the camera and only apply to the illumination.

Master Multiplier – A general multiplier for the diffuse color. It is ignored when the Scattering mode is set to Ray-traced (GI only).

Shadow Strength – A multiplier for the opacity of the shadow that the volumetric casts on other objects.

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