How to set the fluid's mask?

#1

Hello everyone, I have a question about the fluid:

I have two fluids A and B, they are crossed(Overlay).
When I want to render the fluid A, it should be how to set the fluidB’s mask?

If “Matte Opacity” option is set to “Black Hole”(the fluid B):
In the result image:the fluidB’s color channels are black, but the Alpha channel is still white(should be black).

So,what shoul I do ?
Thanks!

#2

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