Removed vertex color mode which was intended to alter the blend mask.

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Material/LayeredLit/TerrainUI.cs

         const string kLayerMaskMap = "_LayerMaskMap";
         MaterialProperty layerInfluenceMaskMap = null;
         const string kLayerInfluenceMaskMap = "_LayerInfluenceMaskMap";
-        MaterialProperty vertexColorMode = null;
-        const string kVertexColorMode = "_VertexColorMode";
         MaterialProperty objectScaleAffectTile = null;
         const string kObjectScaleAffectTile = "_ObjectScaleAffectTile";
         MaterialProperty UVBlendMask = null;
             layerCount = FindProperty(kLayerCount, props);
             layerMaskMap = FindProperty(kLayerMaskMap, props);
             layerInfluenceMaskMap = FindProperty(kLayerInfluenceMaskMap, props);
-            vertexColorMode = FindProperty(kVertexColorMode, props);
             objectScaleAffectTile = FindProperty(kObjectScaleAffectTile, props);
             UVBlendMask = FindProperty(kUVBlendMask, props);
             UVMappingMaskBlendMask = FindProperty(kUVMappingMaskBlendMask, props);
             m_MaterialEditor.TextureScaleOffsetProperty(layerMaskMap);
             EditorGUI.indentLevel--;
 
-            m_MaterialEditor.ShaderProperty(vertexColorMode, styles.vertexColorModeText);
-
             EditorGUI.BeginChangeCheck();
             EditorGUI.showMixedValue = useMainLayerInfluence.hasMixedValue;
             bool mainLayerModeInfluenceEnable = EditorGUILayout.Toggle(styles.useMainLayerInfluenceModeText, useMainLayerInfluence.floatValue > 0.0f);
             CoreUtils.SetKeyword(material, "_ENABLESPECULAROCCLUSION", material.GetFloat(kEnableSpecularOcclusion) > 0.0f);
 
             CoreUtils.SetKeyword(material, "_MAIN_LAYER_INFLUENCE_MODE", material.GetFloat(kkUseMainLayerInfluence) != 0.0f);
-
-            VertexColorMode VCMode = (VertexColorMode)material.GetFloat(kVertexColorMode);
-            if (VCMode == VertexColorMode.Multiply)
-            {
-                CoreUtils.SetKeyword(material, "_LAYER_MASK_VERTEX_COLOR_MUL", true);
-                CoreUtils.SetKeyword(material, "_LAYER_MASK_VERTEX_COLOR_ADD", false);
-            }
-            else if (VCMode == VertexColorMode.Add)
-            {
-                CoreUtils.SetKeyword(material, "_LAYER_MASK_VERTEX_COLOR_MUL", false);
-                CoreUtils.SetKeyword(material, "_LAYER_MASK_VERTEX_COLOR_ADD", true);
-            }
-            else
-            {
-                CoreUtils.SetKeyword(material, "_LAYER_MASK_VERTEX_COLOR_MUL", false);
-                CoreUtils.SetKeyword(material, "_LAYER_MASK_VERTEX_COLOR_ADD", false);
-            }
 
             bool useHeightBasedBlend = material.GetFloat(kUseHeightBasedBlend) != 0.0f;
             CoreUtils.SetKeyword(material, "_HEIGHT_BASED_BLEND", useHeightBasedBlend);

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/LayeredLit/Terrain.shader

 
         [HideInInspector] _LayerCount("_LayerCount", Float) = 2.0
 
-        [Enum(None, 0, Multiply, 1, Add, 2)] _VertexColorMode("Vertex color mode", Float) = 0
-
         [ToggleUI]  _ObjectScaleAffectTile("_ObjectScaleAffectTile", Float) = 0.0
         [Enum(UV0, 0, UV1, 1, UV2, 2, UV3, 3, Planar, 4, Triplanar, 5)] _UVBlendMask("UV Set for blendMask", Float) = 0
         [HideInInspector] _UVMappingMaskBlendMask("_UVMappingMaskBlendMask", Color) = (1, 0, 0, 0)
     #pragma shader_feature _THICKNESSMAP2
     #pragma shader_feature _THICKNESSMAP3
 
-    #pragma shader_feature _ _LAYER_MASK_VERTEX_COLOR_MUL _LAYER_MASK_VERTEX_COLOR_ADD
     #pragma shader_feature _MAIN_LAYER_INFLUENCE_MODE
     #pragma shader_feature _INFLUENCEMASK_MAP
     #pragma shader_feature _DENSITY_MODE