I will read the info there and look into editing the colour proms - perhaps I can find a solution, but otherwise I'm going to have to come up with another solution.The only other thing you could do is edit the colour prom to give a dark colour for one of the pens, they are rrrgggbb i think. Aaron giles discusses it in this link. It's not going to be black though.
Aaron giles
The only other thing you could do is have a background colour other than black, the dark blue of the ghost pupils maybe and build your tiles around that
I'd rather not change the background colour though ... but let's see how it goes