First of all: The file ~/.Xdefaults is deprecated. Please use ~/.Xresources instead.
If it does not exist issue the following command in a terminal:
Code:
touch ~/.Xresources
Then put the following in it:
Code:
xterm*Background: black
xterm*Foreground: white
"xterm" must be all lowercase.
Now in a terminal issue
Code:
xrdb -merge ~/.Xresources
and restart xterm.