title: Create unique list from vlookup or index/match
body: <p>I love VBA but if it can be done with a fairly straight forward formula, that's better! (for the end user's sake)</p>
  
  <p>Let's say I have the following data:</p>
  
  <p><img src="https://i.stack.imgur.com/T2z3A.png" alt="enter image description here"></p>
  
  <p>I'd like to create a formula I can fill down in column [D] that will lookup on "a" (this could also be a row rather than column) and return in consecutive rows (or columns) "red", "blue", "green" - that is consecutively return all unique values and then stop/error out or something... </p>
  
  <p>Possible? Reasonable expectations?</p>
  
  <p><strong><em>Bonus points for explaining how your formula works</em></strong></p>