You can change colors and fonts in xterm using the .Xdefaults config file in your home directory. First, open the file.
vi ~/.Xdefaults
Next, insert the following lines.
xterm*foreground: #FFFFFF xterm*background: #000000 xterm*faceName: Terminus:pixelsize=14
Finally, refresh the settings with the following command.
xrdb ~/.Xdefaults
That's it. You're now using white on black with the “Terminus” font at 14 points.
More settings are available in the Arch Linux Wiki.