Inside the shader used in DrawRenderersCustomPass:
........
void GetSurfaceAndBuiltinData(FragInputs fragInputs, float3 viewDirection, inout PositionInputs posInput, out SurfaceData surfaceData, out BuiltinData builtinData)
{
........
// Write back the data to the output structures
ZERO_INITIALIZE(BuiltinData, builtinData); // No call to InitBuiltinData as we don't have any lighting
ZERO_INITIALIZE(SurfaceData, surfaceData);
surfaceData.color = _Color.rgb;
}
........