NOTES:
* Transparency - or, to use the term used in Scribus, Opacity (the opposite of Transparency) - should not be used to 'make something invisible', and it should certainly not be used to 'switch something off'. There is always a better way to do this.
* If you want a line or a fill to be invisible then use "None" for its colour.
* If you want an object to be temporarily invisible then move it to a different layer and switch that layer off.
* Transparency/opacity should not be used to make a lighter shade of a colour, the "Shade" setting should be used for this.
* PDF 1.3 does not allow for transparencies so anything with an Opacity of less than 100% will be displayed at full 100% Opacity (see attached sample documents: original SLA, PDF 1.3, PDF 1.4, and PDF 1.5).
* Generally it is best to stay away from the Opacity settings unless you absolutely need to use them and you know what the potential problems could be. Not using them means that you shouldn't have any strange results later on.