I am responding to my own question. I searched and searched and found the best recipe to clean our oil base stained cedar wood exterior! The black discoloration literally "ran off" when sprayed with a simple garden sprayer and the following mixture: 1 gal water ( I used warm softened water from inside home), 4 C Clorox outdoor bleach, 1/4 C Dawn liquid dish soap. Am feeling guilty for all the times my husband scrubbed this house! After spraying with the garden sprayer, let it sit about 10 min and rinse off with hose. It looks like new siding! The company that makes our shingles also recommended something similar to clean our roof so we knew the shingles would not be "bleached".

Bump- I have a cedar sauna which was installed 3 years ago. We waited a year to let the oils settle out, washed with TSP and lightly sanded and then applied Thompson’s water seal in clear cedar. Big Mistake! The colour is pink, like a 1970s fence. Within one year, there is massive flaking and green mildew in the joints in the areas in the sun. I am sanding the flaking off where I can. In the places that were protected from light (ie the back), the stuff looks fine. I will try Jennie’s recipe above to try to get the pink out. Question: I think that I need to put a protective stain on it but hesitate to reapply the same product. Anyone have any ideas?

thompsons is the worst. use a better stain sikkens, Armstrong Clark, ready seal is good if you dont want much color use ship and shore from dalys or there teak oil

Thanks! I have used Sikkens in the past on other things so will go that route. I am intrigued by the teak oil too but hadn't thought that it could be used outside.