My iphone 6s screen icons changed into black and white.

Did you check the settings for the color of the screen in Settings/General/Accessibility/ and see if the display for colors is set to grey?

Apply color filters. Go to Settings > General > Accessibility > Display Accommodations > Color Filters, then turn on Color Filters. Or, you can triple-click the Home button, then choose Color Filters. Tap a filter to apply it. To adjust the intensity or hue, drag the sliders.

User Guide iOS 10/Accessibility features

can't access settings on even use the phone

Hi

Go to settings Accessibility turn grayscale off.

Cheers

Brian

thank you brian , but I can't get into the phone to do anything , I have an error 4013