Try using Mothers Back-to-Black or Meguair's Plast-X? Used primarily for black restoration on materials such as that, and with any luck it would help restore that section back to original color, or close enough that when you do the entire dash in the mentioned products above, it would blend it well enough.
It's inexpensive to buy those items anyways, and I use them all the time on interior and exterior trim and moulding