Issue with Subsurface Scattering Color in MaterialX Standard Surface Shader using Karma

[gpss]

Hello everyone,

I’m experiencing an unexpected behavior when rendering with Karma (both CPU and XPU) using the MaterialX Standard Surface shader, specifically related to the subsurface scattering parameters.

Here’s my test setup:

• Base Color: Red (RGB = [1, 0, 0])
• Subsurface Color: Green (RGB = [0, 1, 0])
• Subsurface Intensity: 1
• Radius: {1, 1, 1}
• Scale: 1

Based on my understanding, with these settings I expected the material to display Green (because Subsurface Intensity is 1) as a result of the subsurface scattering. However, the rendered result comes out completely white—almost as if the output is dominated by the scattering (i.e., the Radius parameter), with no visible contribution from the Base or Subsurface Color.

I’m wondering:

1. Is this behavior a known limitation or bug in Karma’s implementation of the MaterialX Standard Surface shader (particularly the subsurface scattering part)?
2. Could there be another explanation or parameter interaction that might cause the subsurface effect to override the expected color ?

Any insights or advice would be greatly appreciated.

Thank you in advance for your help!