My passenger wiper started to discolour where the arm connects to the wiper-blade when it was only around 18 months old, I pointed this out to my dealer but it was dismissed saying I must be using the 'wrong' screen wash! I've only used VW or Quantum. I touched up the etching marks which looked ok but in the end I replaced the passenger one when the hinge started to go white.
Now got the same on the drivers side

The wipers and scuttle area gets a lot of abuse with liquids and full on baking sun, probably why so many go grey after a while unless you protect them.