Colors (a little bit more than you asked, but might be useful for others with the same or similar question)
1. As you noticed, to change color sets (swatches, palettes) in Scribus, all you need to do is to run Scribus, but do not create or open any document. After that, choose a color set in
Edit > Colors, and that color set will be default for all
newly created documents. However, already created documents will retain their respective default color sets. But, since you can import colors via
Edit > Colors, all you need to do is the following:
a) set a new default color set,
b) create a new document and save it,
c) import colors from this new document to your other document(s).
2. The easiest way to add color sets to Scribus from GIMP, Photoshop, or to even add Pantone colors, is by using
SwatchBooker. After installation, you'll notice two application entries:
SwatchBooker Editor and
SwatchBooker Batch Converter. Start the latter.
3. Usage of SwatchBooker Batch Converter is simple:
a) press "Add Files" to find GIMP palettes (.gpl) you downloaded and convert them to format readable by Scribus (.xml)
b) set output directory of your liking
c) in "Format" drop-down list at the bottom of the window choose "Scribus Swatch (*.xml)" and press "Convert"
d) move the newly created .xml file(s) to
~/.scribus/swatchese) start Scribus, press "Cancel" at the "New Document" dialog, so that Scribus is running without any document open
f) follow Step 1.
Patterns
Unlike for color sets, I'm not sure if there's an automated way to have patterns loaded at startup. According to
Scribus Wiki, you can store patterns you'd like to reuse in a new Scrapbook and load them using
Edit > Patterns. But, of course, you can always create a new document template, put into it all elements you want to be loaded when creating a new document from it, save it in
~/.scribus/templates and use "New from Template" instead of "New (Document)" dialog.