Thaks so much for the great tips.
I am filming with the 2.5 K BlackMagicCinema Camera. It performs best at 800 iso but is not a super low light cam.
The rest appears total dark (black) only the abient candles and lights appear in the background. So basically there is no natural light temp. I guess. See the following BMCC frame. I even cranked up the exposure a bit.

Again, anny additional advice would be highly appreciated…