Go to Rubacava in years 2, 3, or 4 and enter the tattoo parlor. Go to the back room with the refrigerator and examine the poster with tattoo designs next to the cabinet. Max (from Sam And Max) and the Corley Motors logo (from Full Throttle) are featured as small designs on the poster.
Save the game during an intermission sequence (such as when Carlie comes to claim the suitcase from Manny), then load that saved game. Some characters will be invisible, and you can only see the face of the character when it speaks.
Press F1 to pause game play, then press ALT + TAB to go to the Windows Desktop. Go back to the game and you will notice that the previously black and white paused screen will now be in color. Also, all characters will have disappeared.