OctaneRender® uses vertex colors or other vertex attributes while rendering materials. OctaneRender® loads and interpolates both real numbers and colors over the scene's triangles and sends them to the OSL shaders.
Figure 1: Accessing the Vertex Color tool in Blender®
After you create a Vertex Color index, you can use it's name as a reference in a Color Vertex texture to render the vertex paint in OctaneRender®.
Figure 2: Referencing a Vertex Color index name