To preserve the natural color of the wood, use an exterior semitransparent oil stain. It seals the wood while allowing the grain and color variations to show through. And its pigments add an overall color tone. Make sure the stain contains ultraviolet inhibitors, which will slow down bleaching by sunlight, and a mildewcide to slow fungal growth. Look for samples on cedar at the paint store, or bring in your own piece of wood to test. A test sample is the best way to ensure a satisfactory result.
Power washers are aggressive. They’ll strip the wood as well as clean off the dirt and grime, but you can also erode the wood too deeply and ruin it. The key is to use the right sprayer tip and technique. In any case, the power washer’s spray will slightly raise and roughen the grain on smooth wood. That’s actually good—it allows more sealer to soak in and improves the finish.