Morthoron, there's enough examples on here now to show that Tolkien equating light with good, dark with evil was anything
but consistently shown!
And to add that the Gondorians built Orthanc out of black stone and the walls of Minas Tirith too. I believe that white flowers grow in Morgul Vale, and Saruman's symbol is the White Hand. Far from setting up a simplistic white/black symbolism Tolkien plays with the perceived cultural notions of white/back = good/evil - not all shades of black are bad, not all shades of white are good. It's been brought up many a time to counter the accusation that Tolkien is simplistic and uses traditionally racist symbolism.
Course if you want to just win an argument or make a point you may disregard all these examples which show Tolkien was not being so straightforwards.
Yes there are contrasts, but they are by no means fixed - Tolkien also turns traditional contrasts upside down.
Rather than comparing white and black or light and darkness, and equating these with good and bad, what Tolkien does is set up the contrast of Light and Unlight, neither of which require either brightness or darkness, black or white. A very different thing altogether. In his world darkness can be very beautiful - Varda's stars against the night sky for example, or Arwen's hair, and brightness can be horrific - the bright flames at the heart of Mount Doom or the awesome Balrog.