I have a rough sawn 2x8 cedar board I'm going to use for a mantel and I really like the color and rough cut . It will be indoors out of direct sunlight. Does it need to have a finish applied to preserve the color and protect the wood ? If so, what to use that won't change the color or characteristic of the wood ? -Thanks

Clear finish

The back of the wood is the place to test. I am a Boiled Linseed oil guy. Tung oil, and many others good protectants exist. I did a 4x6 cedar mantle at the cabin with BLO, it is clear. It can be touched up in a few years with a alcohol wipe down and a fresh rub of BLO, without stripping or sanding old finish. But test your ideas on the back.

It depends if the rough cut cedar is clear or weathered to start, it will take on a different appearance solely based on that. Below are a couple mantel pics that I finished for my cabin, the 1st pics for our family room mantel are aged/weathered with clear poly only- the color turns to a bourbon hue (my desired effect). The last pic is our cabin screen porch and you can see the contrast between the clear cedar box car siding and weathered mantel- both finished with clear poly only.

Satin, semi, or gloss ?

I personally prefer satin because it has less sheen, I would also build up a couple of coats- it's almost impossible to remove airborne dust from a rough sawn mantel over time without a 2-3 coats of build-up

Not related to the topic but I just completed a mantel for my daughters new house and the beam I found had a bullet lodged in it- I finished it with the bullet in place, they thought it was kinda cool.