I am building a new cedar greenhouse and would like to preserve the natural color of the cedar wood.Are there any known sealers or non toxic paints that I can use ? ,Help!!!

Preserving the natural color of the wood will depend upon how much direct sunlight it is exposed to per day. The more sun exposure the more bleaching effect that will happen. Chances are, the more UV blocking ability that you want, the more toxic you will get. I suggest researching your local paint stores and see what they have to offer. I seal the horizontal portions of my deck every year with boiled linseed oil. It works great and is cheap if you buy from the right source.

Thanks, I will look around. I am in zone 6, so there is less sun exposure.Is linseed oil safe in a green house enviroment?

I don't know if it posesses any toxic qualities. I use it all the time and never payed attention to it. Linseed oil has been used as a wood preservative for at least a hundred years. I have personally used it to oil gun stocks, had it all over me as a kid. Nothing's wrong with me now, I think. I don't see how it could contaminate your soil, unless you plan on incorporating part of the frame with boxes directly exposing it to the soil. I think I have a can out in the barn, I will look at the warning that says not to drink it and check. I'll get back to you on that.

Went out to the barn and checked that can today. The only caution on it said; do not injest and a warning about oily rags and spontaneous combustion. That was it. I don't see why you couldn't use it.

Thanks, I appreciate the info. I will try it.

One of the strongest factors that would age and destroy the surface-layer of your wood is UV exposure, so something with a strong UV blocker is a must. Mixwax has something called "Helmsman Spar Urethane", which does contain a blocker. Read carefully the cautions on this one: it will be fine for your greenhouse after it has dried, but has some toxicity during application. I've been having great success with Muralo's deck stain/finish - I believe you can get it without stain. Wooden decks get about the worst punishment of anything, being horizontal & outdoors. I'm thinking of gathering some different finishes together and doing a multi-year comparative test, & put photos of the result on a webpage. Lots of woodworkers could use the infor.
btw, I am told that there is as yet no perfect UV-blocking clear protectant.
Best of luck

Aren't there some safer wax based deck treatments that could be used?

Any sealant used outdoors is temporary, especially if it is used on horizontal surfaces. Best bet is to use a weather resistant wood with no sealant and accept the color change. We have had the best luck with black locust and that is what we are going to use for our greenhouse, deck and solar kiln. It's considered a trash wood so it is very cheap, grows everywhere around here quickly (hopefully the secret won't get out!) The nature conservancy used black locust with no finish to build their decks at a marshy preserve on the Eastern Shore of Virginia (some of you may have walked on it?) When it is fresh it is a beautiful honey color, we bought black locust flooring for part of our house. It was cheaper than vinyl and has mellowed into a deeper honey color!! Outdoors it weathers to a grey color and lasts almost forever. Many farmers use it for fence posts and barn poles. Good luck with whatever you decide to do!

Funny you should mention Black Locust. I have never seen a Black Locust tree since I have been here on the east coast. When I was growing up, I lived in Missouri and Oklahoma. They grew everwhere. It was a dangerous tree to be around. The entire surface of the trunk was covered in rows of thick black thorns, some reaching 8 to 10 inches in length. As kids, we would use the thorns to fashion frog gigs at the end of a lance. Sometimes we would make arrow points out of them as well. Other than that, we would avoid them.