What happens if you enable transparency using btn.setTransparency(TransparencyAttrib.M_alpha) ?
Also, in your code snippet, you are setting test.setAlphaScale on a string, which has no such method. I assume the code you used in your application looks different?
That’s because it makes a copy of the NodePath you pass in. You could however try passing in geom_color=(1, 1, 1, 0.5). Otherwise you will have to either set it on the frame itself or access the underlying OnscreenGeom component and set it there.