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Burning wood in a gas fireplace constitutes a serious life-safety hazard.
In General
Using a fuel other than that for which a fireplace is designed may ignite a structural fire in the surrounding construction and/or discharge toxic gasses into habitable space.
Discussion
Gas fireplaces are fuel burning appliances. Each fireplace is constructed to handle the heat and other products of combustion produced by specific fuels. Each fireplace is designed to distribute heat and discharge the products of combustion safely both in the moment and continuously over the life of the building.
A gas fireplace operates within well defined parameters and is an engineered system. It is not designed to handle the byproducts of a wood fire, it is not designed to properly draft a wood fire, and is not designed to operate over the range of possible temperatures that a wood fire may produce.
Sure, Anything is Possible...But
If sufficient resources are devoted to conversion, it may be possible to 'replace' the gas fireplace with a wood burning one. However, doing so is likely to entail significant demolition, construction, time and energy.
Creating a safe wood burning fireplace will always require experienced expertise and substantial craftsmanship.
Best Answer
Yes. These are painted all the time. I just used this for a traditional wood burning fireplace. You can search for fireplace paint but really you are looking for it to withstand the max temperature. Since yours is gas I am guessing your max is well less than 1000 F.
Also most fireboxes are painted black so you can see the fire easier. And because of the heat a lighter color may get burn marks in it from the heat.