Displacement Reaction

I found these two videos on displacement reaction from youtube.com. It's quite interesting! Have a look...



(1) Reaction between silver nitrate solution and copper



(2) Reaction between copper sulphate solution and iron nail
For the first reaction, reaction between silver nitrate solution and copper

• copper is more electropositive than silver
• copper displace silver from its salt solution
• the silver solid, silver is displaced by copper from its salt solution
• Chemical equation:

     AgNO₃(aq) + Cu(s) --> Ag(s) + Cu(NO)₃(aq)

Question: Why does the colourless solution turns blue?
For the second reaction, reaction between copper sulphate solution and iron nail

• iron is more electropositive than copper
• iron displace copper from its salt solution
• the brown solid, copper is displaced by iron from its salt solution
• Chemical equation: 

      CuSO₄(aq) + Fe(s) --> FeSO₄(aq) + Cu(s)

Question: Why the intensity of blue copper sulphate solution decrease?
Points to ponder: Why both reaction are examples of redox reaction?