MASH’s color node is based on the color per vertex of Maya’s particle system and can display nicely in the viewport but it’ll take a couple steps for it to appear in a software render of your choice. One, to export the vertex colors from the shape node of the reproMesh, and then to assign a utility node for your renderer to read the vertex color information.
Here’s how to do it for Arnold:
1.1 Under the ReproMeshShape node attributes tab:
1.2 Check “Export Vertex Colors”
2.1 Assign an Arnold shader
2.2 Click on the “checkerbox” on the Color channel under the Diffuse tab
2.3 Choose the Arnold utility shader node “aiUserDataColor” in the “Create Render Node” pop-up
3.1 Under the “aiUserDataColor” attributes tab
3.2 Type in “colorSet” in the “Color Attr Name” field
That’s all! Hope that helps!