Lovely set up! If I was to throw my 10 cents (this site even has me using American money now) I would opt for a darker substrate and dark background.
This would give the fish a little bit more security and could perhaps bring out colours even further and initiate even more natural behaviours.
Here is my firemouths before and after I was helped with this
You can just see one on the left.
This was taken just now. I subdued the light, added plants, changed the substrate and added a background. As you can see they no longer hide and there colours have significantly changed
Sent from my iPhone using Aquarium Advice