you can't disable the END key (red phone button) in Nokia phones as the specification says implicitly that END key must destroy the MIDlet. What the END key does (in Series 40) is that it calls your MIDlet's destroyApp() method, where you can yourself implement e.g. an auto-save feature with which you store the game state to RMS (important variables, etc.) and allow the user to resume from the same position when the MIDlet is run next time. There will be e a technical note about this later at our web site, stay tuned.
About the TextField color, you can't change that. All high level UI layouts and colors come directly from the underlying platform. Please check MIDP 1.0 specification for further details.