The Solid Color blend node is used to add a single color to the composite node tree. In figure 1, The Solid Color node is used to add a white background behind the cube and the ground plane which has a Shadow Catcher material applied to it and Alpha Channel activated in the Kernel parameters.



Solid Color



Figure 1: The Solid Color node used to add a grey background in the transparent areas behind the logo and its shadow catcher


Solid Color Parameters

Enabled - Determines whether the Solid Color node is active or not.

Color - Specifies the color. 

Alpha - Specifies the level of opacity for the Solid Color.

Effects - Provides the ability to stack additional Output AOV nodes to this node using blending settings.

Blending Settings - Provides typical blending options used in the compositing process.