[vtkusers] How to blend RGB and gray image

[Anka Kochanowska]

Hi!
I capture UltraSound image which may be RGB and I want to blend it with 
the correspoding data image which is grayscale.

        m_blendedImage = vtkImageBlend::New();
        m_blendedImage->SetOpacity(1, 0.75);
        m_blendedImage->AddInput( 0, m_videoSource->GetOutput()); //RGB
        m_blendedImage->AddInput( 0, 
m_displayWindowLevelColorsImage->GetOutput()); //gray
        m_blendedImage->Update();

The output is grayscale.
How could I get a color output? Any examples? (I am not an expert.)

Anka