After the power button is switched on my phone is displaying in black and white asking for password. How to change the color of the opening screen as seen in the picture?
Have you set up a password lock on your LG Optimus L7? If so, you have to disable it first for it to stop showing up every time you press the switch to turn it on. Here's how.
From your home screen, bring up your Optimus L7's apps by pressing the button for the app drawer -- that onscreen button on the lower right corner of the screen that looks like a window -- and look for Settings. Under Settings, scroll down and press Security, then press Screen lock. You may have to enter your password first to get through.
Once through, you should see an option that says None at the very top. Select that option and test if you were able to disable the screen lock by pressing the power button. That should fix it!