I have spent a fair bit of time walking over, under, and through timber trestles. If they are well maintained, and not neglected after, say, 25 years or more, they should be a deep tan colour, almost black when the timbers are first installed. In fact, every trestle that I have encountered has parts of the same length of timber lighter in patches, and then other areas are coated with a treacle-like pitch.
Cedar weathers nicely naturally if it is left untreated, and it does indeed turn a silvery feathered appearance by the end of the second summer. It then takes many years to decay to the point where it is unsafe for a load. Its natural oils protect it from decay and water penetration. Burns smokey.
I take joy in letting folks know that I actually used real creosote oil on my one scale trestle. It took surprisingly little for the stuff to penetrate the wood I used. Under the lights, it looks great, but it is much lighter in images...don't know why. The abuttment cribs are not creosoted, but stained with a heavy wash of burnt umber and some grey. Yet, in most images, it almost looks like natural wood untreated, or else splotchy. Oh, well...