volume rendering independent component color problem

I am using independent component with vtkOpenGLGPUVolumeRayCastMapper or vtkGPUVolumeRayCastMapper to represent the volume and the labels.
vtk version is 9.1

the first independent component is the labels and its value is :

  • 0 if no label , color set to white
  • 1 ia a yellow label
  • 2 ia a blue label

the second component is the volume

I have problem with the labels colors , if i set the first label opacity to 0 the second label appear fine

if the first label opacity is set to 1 both labels appear yellow as the first one, even if second label opacity set to 0

I noticed that while interacting with volume the color keep changing ,
the first label change between white and yellow
the second one change between yellow , blue and white