I think this kitchen would be well served with a glass backsplash. Something modern looking - perhaps rectangular stacked vertically with no offset. Or even just a glass sheet - not tiles. All one color to keep it looking clean and sleek. In terms of color I'd choose something that ties the room to the rest of the house. A soft white or green or blue perhaps. There's a lot you can do with this.

Beautiful re-use of existing materials - good for you for saving it!!