The 'Undo' feature in Word (shortcut Ctrl + Z) allows you to revert changes, including the black and white conversion, step-by-step, back to the original state of the image. Keep in mind that the 'Undo' feature has a limit on the number of actions it can reverse, so it's best used immediately after making changes you wish to revert. If significant changes have been made since the conversion, using the 'Reset Picture' option may be more effective.