In Star Wars a new Hope Luke's lightsaber has a light blue, however in the prequel films the same blade is a dark blue.

Here's the blade in A New Hope

![enter image description here][1]

and here it is in Revenge of the Sith

![enter image description here][2]

Is there an in universe reason for this change in colour or is it simply a byproduct of the newer techniques of making the lightsabers?


  [1]: https://i.sstatic.net/1O3ba.jpg
  [2]: https://i.sstatic.net/kcEjs.jpg