Whoa.. that kuhli looks massive :D
To be honest, I'm not sure that I'm overly keen on the mixture of white sand and black gravel - it's just too much of a stark contrast.
The main thing though is that you like it, and if you're happy with it then I'd keep it the way it is.
If it were me, I think I'd be tempted to replace all of the sand with black gravel. Either that or have gravel on both sides with a path of sand in the middle leading to the centre of the tank.
That looks like a nice hiding spot you have there for the firemouth :)