This page gives detail about the Reflection Highlights Color Channel.
Overview
The Reflection Highlights Render Channel returns a grayscale image that corresponds to the value in the Highlight Glossiness of the materials in the scene.
Since V-Ray Next, reflection highlight glossiness can no longer be controlled separately from reflection glossiness in VRayMtl. This render element now contains the same information as Reflection Glossiness .
UI Path
||Node Editor|| > Add > Render Channels > Color Channel > Type > Reflection Hilights
