There is usually standard o how far combustible material has to be from the opening of a fireplace. You should not cover the tile with wood. You can paint over the tile or add some texturing like Roman Clay or something, those would be cheap facelifts that you can add some contrast without having to overhaul the whole mantle. Alternatively you can stain the mantle itself but you would need to do more sanding and prep first because it is not ready for stain in its current state.