title: Colour fill all cells that match any date in a column
body: <p>I would like green background fill to be applied to any cell - in entire sheet - whose date has a match in column C. I tried:  </p>
  
  <blockquote>
    <p>=VLOOKUP(<strong>A1</strong>, C1:C15, 1)  </p>
  </blockquote>
  
  <p>but this works only for the specified "search key", A1, so I'd have to repeat the formula for each additional cell and there are way too many. </p>
  
  <p>Perhaps this requires an Apps Script. Any Ideas?</p>