Play Level 61 ("X Marks the Spot"). This level is basically a single rainbow pyramid in the center of the landscape. You must shoot the pyramid. If it doesn't come up purple, kill yourself and try again. Eventually, you'll get a new pit in the center of the X. Next, fall into that pit. Then go to the level grid and choose a level with limeys. From then on, until the next reboot, the limeys will have a very crazy new look.