I want to superpose white blue green and black contours but coloring and hatching the interior of the contours with the exterior of the contour staying empty instead of being white.

My contours

All I have found is this where they manually build a colormap with an alpha set to zero for the white values but it seems a bit complicated.
Does anyone know a simpler way to do what I want (for example if contour have a “fill” functionality or if contourf can have a varying alpha for the different regions)?