As the title says - or perhaps make A4 the default?

To expand, tex-live and other distributions have a default paper size, that can be set by the user, and which seems to be respected by pdflatex and latex.
However packages like xcolor and geometry (used in the latex template) will change the paper size to letter, unless the size is forced by setting it as an option to the document class.

I assume it is possible to work around the issue by making my own custom template. I don't think that it is a reasonable solution though - it seems like a bit much just for standard paper.