User-defined colors in /etc/X11/app-defaults/XTerm

[Fergus Daly]

I am completely drowned by the volume and complexity (and in some cases antiquity) of responses when googling [variations on]
"xterm color": e.g. multiple references to all of .Xdefaults, .Xresources, .xinitrc and much much more.
I do not have any of these. Using xterm within Cygwin the file /etc/X11/app-defaults/XTerm seems to serve all required purposes relating
to color. I have (comments # below are not part of the file):

xterm*color3:         orange      # for selected text using Find/Replace in nano
xterm*color10:        darkgreen      # for binaries and any *.sh using ls
xterm*color12:        blue      # for folders using ls
xterm*color13:        maroon      # for sockets using ls
xterm*color14:        brown      # for links using ls

xterm*color1:         purple      # cant find any instances of these 4 being used but often see them in online examples of XTerm
xterm*color2:         tan
xterm*color6:         yellow
xterm*color11:        red

Question 1 I'm not inclined to mend what isn't broken but do others find this file and its location a convenient or even a
recommended way to control the palette? 

Question 2 I think there are 16 settings available (xterm*colorNN, 1 to 16) but nowhere have I been able to find a reference describing
what each controls. Can anybody please point me to such a reference?

Question 3 In minty not xterm I get pretty much the same thing (sockets are shown purple not maroon; selected text in Find/Replace in
nano is shown red not orange), but think this is just coincidental.
I have no idea where mintty in Cygwin (or bash - all different again) get their colors from. Please can anybody say?

Thank you!