Changing the color of fire

I don't know if that program at ModTheSims would help with the flame's color. I think it's for the flame's behavior in-game. Its animation, I mean.

Re: fireplaces. There is a lightmap texture that the game displays when the fireplace is lit up. You could change the lightmap to be green. And there is a light resource in the warehouse; when the fireplace is lit, it casts light as a lamp would. You can change the color of the light in the warehouse.

As for the flames themselves, the resource for that doesn't appear to be in any of the game's fireplaces so I think you'd have to dig into the game's core files to find it. If you changed the flames, likely it would affect every fireplace. I don't think there's a way to force a fireplace clone to reference a custom fire effect as far as flame colors are concerned.