How to make two colors transparent

[Dufusyte]

Let's say I have two colors I want to make transparent (say, Blue and Red).

My first guess was to use Selective Color Correction to make both colors the same, i.e., make the Blue Red, and then once they are both Red, just use the Chroma Mask to make Red transparent.

This did not seem to work; it appeared that the Chroma Mask was working on the original base values rather than the Selective Color Corrected values, so it was not recognizing that Blue had been changed to Red.

Other attempt was to use Selective Color Correction to not merely change a color, but to change its transparency. This also did not appear to work.

Any tips on how to make two colors transparent?

[SBowie]

It does look as though the order of operations is such that the keying is done prior to color correction, which means this approach won't work. And none of the color correction tools offer alpha adjustment, so that's out too.

Seems the only way to do this natively would be to use two passes - either two keyer passes, or one color correct and one keyer pass (rendering the first pass before adding the second operation.)