Getting a red, green, and blue screen when trying to hard reset

First, if you haven't already tried it, please remove and re-insert the battery.<br /><br /><b>The following method erases all data from the handset's memory, and sets it back to original factory settings. It does not erase the sim card or the memory card. </b><br /><br />There are two ways to perform a Factory Data Reset, also known as a master reset or hard reset. Since we cannot boot into the device, we will perform a hard reset:<br /> <ol> <li>The device must be powered OFF to perform this reset.<br /><b>Note: </b>If the device is not responsive and does not turn off, remove the battery and re-insert it. </li> <li>Press and hold the <b>Home</b> button (picture of a house on it) and the <b>Power</b> button (the red hang-up button) at the same time.</li> <li>Keep holding <b>Home </b>and <b>Power </b>together for at least 25 seconds, even if the "Startup" screen appears.</li> <li>Release the keys when you see a black screen with a warning sign.<br /></li> <li>Slide the keyboard open.</li> <li>As a shortcut, press <b>ALT+W</b> to factory reset the device. If this does not work, continue with the below steps.</li> <li>Press <b>ALT+L</b>.<br /></li> <li>Press <b>Alt+W</b> for 'wipe data/factory reset'.</li> <li>Press the <b>Home</b> + <b>Back</b> key.<br /></li></ol>

Hard reset or Factory reset will restore the phone back to its factory settings; the way it was when it was first bought or the way it was when it left the factory.
Note that this will erased the entire phone's memory (NOT memory card) and settings to the way it was when it was first bought.

How to hard reset or factory reset T-Mobile G1 phone:

1. Switch off your G1. *If it won't your phone won't switch off, take out the battery and reinsert it after a few seconds.
2. Now press the 'Power' key and 'Home' key at the same time and hold it for 20-25 seconds.
3. Then you will see on your screen a yellow triangle with an exclamation mark in the middle.
4. After that, press 'Alt+L' key on the QWERTY keyboard (to clean the phone completely).
5. Next, press 'Alt+W' key (to factory reset it)
6. Again, press and hold 'Power' key and 'Back' key at the same time for 20-25 seconds.
7. The reset is complete.