You can modify the background color, foreground color, font used, window size, and more by editing the .Xresources file in your home directory.  If this file does not exist, you will need to create it.

Also note that you must type the command 

xrdb -merge .Xresources

from your home directory to have X reread this configuration file, and you must restart Emacs before the changes will take effect.

Sample .Xresources file:

emacs.background: Wheat
emacs.f	oreground: Black
emacs.pointerColor: Blue
emacs.cursorColor: Red
emacs.bitmapIcon: on
emacs.font: fixed
emacs.geometry: 100x45