This dialog controls the diffuse color of the smoke, it is now called Smoke color. The diffuse color needs external light to become visible, this is why all the lighting controls are place here. In general the diffuse color may be static (simple color), may be a function of any physical channel, or may be sampled by a texture.
Based on (MXS: darg) - the channel used to determine the smoke color. By default it is simple color, because in the real world smoke has constant color.
Texture (MXS: dtxt) - if the source channel is set to "Texture", this slot specifies the texture.
Reset - resets the settings to their default values.
Modulate (MXS: mod_d) - when the Source is not Texture, this checkbox allows the Source to be multiplied by the texture in the Texture slot.
Simple color (MXS: simple_color) - if the Based on parameter is set to Simple Color, this color is used.
Particle mode secondary bounces (MSX: pmbounces) - V-Ray specific. When checked, this option optimizes the calculation of GI for the smoke. In this mode the opacity is interpreted as a probability for the absorption of the ray, like photons in real light.
Subdiv reduction (MXS: subred) - V-Ray specific. Because the smoke renders relatively slower than the diffuse geometry, one may need different light quality for them. This option reduces the light sampling, dividing the shadow rays count by its value.
Light cache (MXS: lightcache) - enables light caching for each point of the grid. This feature may produce artifacts when the smoke is very dense.
Scattering correction (MXS:difmul, noscatter) - allows the user to disable the scattering of the rays in the volume when GI is used. It also allows selecting how to the light will be calculated. When the scattering is disabled the additional multiplier can be used to adjust the the brightness of the diffuse color.
Enabled - the scattering is enabled
Disabled - the scattering is disabled and the multiplier is used to correct the brightness
Analytic - an analytic formula is used to calculate the contribution of the scattering to the illumination
Analytic+shadows - same as Analytic but geometry is also affected via the shadows
Color gradient (MXS: dcolorx_s,dcolorx_t, dcolorx_v, dcolory_s, dcolory_t, dcolory_v) - The color of the smoke as a function of the selected channel's value.