those guard two different things...shallow zones guard flats/drags...purples guard deeper and protect the sideline behind the shallow zone.
so if ur coming across a defense using purples, throw to flats....if ur coming across a d using shallow zones, look for routes to get behind it..slant outs, wheel routes, posts to sidelines etc...
if ur coming across a d using both purple and shallow zones, attack the inside using slant-ins, in routes, posts over middle.. do this while using streaks that will stretch the d vertically driving the deep blue zones and yellows back, allowing the middle to be open behind the yellows or underneth the yellows.
cv2- attack deep
cv3- attack over the middle behind the yellowsor behind the shallow zones on the sideline
cv4- attack short or over the middle behind yellow