I would be very glad if someone could explain what the
1: before the package name signifies.
1 is the RPM epoch number. It overrides the normal comparison order on version checking. So, if there is some odd reason why you as a packager want to mark a lower version number as an upgrade, you can tag it with an Epoch number.
yum info xorg-x11-xauth Name : xorg-x11-xauth Arch : x86_64 Epoch : 1 Version : 1.0.9 Release : 1.el7 Size : 30 k Repo : base/7/x86_64 Summary : X.Org X11 X authority utilities URL : http://www.x.org License : MIT Description : xauth is used to edit and display the authorization information : used in connecting to an X server.