What colors must flashing lights show to warn of unusual traffic hazards?

• Red or white to the front, amber to the rear
• Amber or white to the front, amber or red to the rear
  Explanation:

  "Widespread flashing lights may be used on any vehicle to warn of unusual traffic hazards; must show flashing amber or white to the front and flashing amber or red to the rear and must flash simultaneously."
• Amber or red to the front, white or red to the rear
• White or amber to the front, white or red to the rear