Why have humans not evolved to see 16 different colours like the mantis shrimp?

Question: Why have humans not evolved to see 16 different colours like the mantis shrimp?
- Keywords:
  evolution,
  shrimp
Asked by anawesomepersonlol to Claire on 27 Jun 2013.
- Claire Lee answered on 27 Jun 2013:
  
  Because, pretty much, we didn’t need to 🙁 Presumably those extra colours or whatever they are give the mantis shrimp a particular advantage in its life. We are pretty much at the top of the food chain as we are (thanks to, eg, our brains) and we can see all of our major predators with the eyes we have.
  
  How awesome is the mantis shrimp!?!

Question: Why have humans not evolved to see 16 different colours like the mantis shrimp?