@**Default816 - **Thanks for the report.
Can you compare your setup with the sample project’s RGB masking example (the second Landscape painting booth)? That example accumulates each channel separately.
Ideally you shouldn’t need to use any special MatLayerBlend nodes at all, just the additive brush should suffice.
One difference is that the no decal is used in that example, though I can’t think of a reason yet as to why that matters yet.