title: 0-1 Knapsack with additional restriction (colored items)?
body: <p>I'm working on this problem mostly out of curiosity in my downtime at work.</p>
  
  <p>Imagine the normal 0-1 Knapsack problem, except all the items are either yellow, red, blue, or green, and due to your OCD you must have exactly 2 items of each color in your knapsack.  So instead of the normal items each item has 3 properties: Weight, Value, Color.</p>
  
  <p>Is this even still a knapsack problem, or is it better define in some other way?  </p>