Can I safely change the color of the flames in my fireplace?

You can do anything but you probably shouldn't. Pretty colors are achieved by adding metal salts to your flame. Most of the pretty colors are from metals that are toxic but some aren't too bad.

Calcium - red (weak)
Boron - green (strong)
Potassium - violet (weak)
Sodium - yellow (very strong)
Zinc - turquoise (weak)

If you are burning wood, keep in mind that soot produces a very intense yellow-orange color from it's blackbody radiation that overwhelms the relatively weak emission from these metals. Hot blue flames are best to visualize colors of this type but that type of flame isn't usually the type you produce in your fireplace. Potassium, calcium, sodium and zinc are already present in wood so if you can't see them already, adding more won't likely help you. Also keep in mind that whatever you add that produces color eventually becomes a finely divided aerosol (ash) that will contaminate your fireplace ashes, chimney, environment and perhaps your indoor air. You run the risk of inhaling finely divided metals and coating everything in your home with them.

I wouldn't try it. Too much risk IMO.

 

Read this : http://chemistry.about.com/cs/howtos/a/aa052703a.htm

 

I assume you have a proper chimney ventilation system. Because the commercial fire colorant are the same thing. And I don't believe that they are much toxic compared to heavy metals, if very very small amount of oxides are inhaled.

 

The real problem is that most of the metals in the product don't go anywhere. They remain in your fireplace ashes. You absolutely cannot clean your fireplace without spreading that stuff around. Also, the interior of the chimney and the cooler parts of the fireplace will become heavily contaminated. Of course you wouldn't want to inhale any gases or aerosols from the fireplace that might waft into the room either.

Contamination like this in the environment eventually goes away but in the protected environment of the home, it will remain until actively removed by scrubbing, carpet replacement, painting etc... This type of exposure is nearly impossible to quantify unless you are actively looking for it. And who does that?

 

It's likely that the green came from the talc (magnesium silicate) used to dust the stick of gum. Magnesium burns with a green flame.