How can a driver know that a snowplow is working ahead?

• They are equipped with flashing amber and red lights to make them more visible.
  Explanation:

  "Snowplows are equipped with flashing amber and red lights to make them more visible. Remember “flashing amber and red means snowplow ahead.”"
• They are equipped with flashing red and purple lights to make them more visible.
• They are equipped with blue and green lights to make them more visible.
• They will be honking the horn continuously while working.