Hi [NAME] welcome to this free user-to-user Alienware laptop discussion forum.  Please enter Service Tag into Dell Alienware M14xR2 Keyboards | Shop Dell Alienware Parts (parts-people.com) and this database will tell you which DP/N Keyboard is installed within your Alienware M14x R2. The seller's DP/N keyboard should match if it is a compatible replacement.  Have a look on YouTube to see if there is replace keyboard video.  The Alienware M14x R2 Owner's manual is Alienware M14x R2 Owner's manual (dell.com). 
Good Morning,  Keyboard of my old Alienware M14x R2 system was not working and I am able to find a replacement, but the seller has asked about the connecting cable color if it is blue or green (some compatibility issue).  Is there any way to know it without opening the laptop please, looking for your advice.  Thank you 
M14x R2, keyboard replacement