This page gives some basic details about the Custom Color Render Element and how it is used in compositing.
The Custom Color Render Element is a generic render element container used for referencing other render elements of type RenderChannelColor containing color information .
||Render Settings window|| > Render Elements tab > Custom Color
The parameters for this render element appear in the Attribute Editor under Extra V-Ray Attributes.
Enable – When enabled, the render element appears in the V-Ray Virtual Frame Buffer.
Deep output – Specifies whether to include this render element in deep images.
Alias – Specifies an identifier for the render element. This can also be used to reference other render elements through their Vray Alias [vrayRE] attribute (found in Extra Attributes rollout; not the cleaner Extra VRay Attributes rollout).
Name – The text added to the end of the rendered file, when saved as a separate file (e.g. myrender.custome_color.vrimg).
Apply color mapping – Applies the color mapping options specified in the Color mapping rollout of the VRay tab in the Render Settings window to this render element. This option is enabled by default.
Filtering – Applies the image filter to this channel. Image filter settings are in the Image Sampler rollout in the VRay tab of the Render Settings.
Denoise – Enables the render element's denoising, provided the Denoiser render element is present.
This render element is not supported with V-Ray GPU rendering.