stove burner distance from back wall and other questions

Just had a multi fuel burning stove installed recently. The installer lined the inside of the chamber using a pink board which I assume is fire resistant. The installer also lit a small test fire to make sure everything is working properly. So the questions I have:

1. The pink board behind the top of the stove and behind the flue have discoloured and turned black after the initial test fire. We haven't lit a proper fire yet. It looks like the board discoloured due to the heat. Are these pink boards supposed to do this or is it an indication that it's too close? The back of the stove is only 30mm from the pink board. Is this too close?

2. Am I supposed to paint the pink boards with fire resistant paint? Would the paint discolour like the boards?