A translucent or semi-transparent oil based stain is a good choice. There is a lot of different semi-transparent stains on the market. Each makes great claims.
The best finish that I can recommend is Sikkens Cetol. This is a great translucent exterior wood finish that looks great and adds very little color. Sikkens products are more expensive than most but are worth it.
No matter what type of finish you choose always test it on a scrape piece of siding. This way you can see the color and effect before committing to any given product.