How do you make the background part of a two-color fill Transparent? This used to be easy.

Hello,

I can't for the life of me, figure out how to make the background part of this Two-Color pattern fill to be transparent.  And it's not under the Transparency tab.  That doesn't work.  That causes all kinds of weirdness.  This used to be super easy back in the day.  Now I have no clue how to do it.

Just to be clear... I want the white and light blue mass, to be just light blue stripes with transparency everywhere the white is.