If it is the lamp, then you can change the light manually. Get a lamp that casts the kind of light you want and check its light name in the Light Names #STR, and then the values for the light colour in the Lighting Point resource. Copy these to your lamp, and presto! New colour light.
But if it's the wall deco, then yes, it's all in the TXMT. The stdMatEmissiveCoef, to be specific.
I tried cloning the lights from Atavera - that works but its a red light. I really wanted the flamingo with its five light colors..... The flamingo has a lighting file - like that round circle light from NL. Neither have a diffuse light when I clone.
Remember how I didn't manage to figure out different coloured diffuse lights for my plumb bob lamp? Yeah. Unfortunately I still have no idea what it is that goes missing from the clone that makes it not have a diffuse light. I'd be happy to investigate, but I fear I'm not much smarter now than I was when I made my lamp.
BTW, that's a really cute little neon fish.
But this sounds like a good solution! Just out of curiosity, could I possibly see the one with the red diffuse light? 'Cause now I really want to know why that one works when nothing else does (which of course isn't to say that I'll be able to figure it out).