VIP Alpha Blending Mixer and transparent color?

Hi

I use Terasik DE2-115 FPGA Cyclon IV board (Quartus 11.1)

I'm trying to use the VIP Core Alpha Blending Mixer based on tPad_VIP example from Terasic.

Layer 0 is a plain black background. Layer1 are clocked video input and layer2 are text overlay.

Text layer1 superimposed on a layer2 of the video stream without Alpha Blending.

All is well, but the text layer background is not transparent and closes the video stream.

Can I set the transparent color text layer?

I need to display text and graphic information over the video stream on a transparent layer.

Or it is necessary to use Alpha Blending?

Thank you.