gnome-terminal and konsole both have options for background (fake) transparency.
Konsole: Settings > Schema > Transparent, Dark Background (or Light Background, depending on the background you have).
Gnome Terminal: Edit > Current Profile > Effects > Transparent Background
(The instructions may not be 100% accurate, depending on your version of the respective X terminal program. In case of doubt, just look around the settings for those two and you should find somewhere to toggle transparency).