Moldy roof

Pure bleach and let it soak is about the only thing I've found to get it semi-clean.

Beer. The more you drink, the less you care about the dirty roof. :)

My coach is parked in my driveway under trees for 3/4 of the year...and in the humidity of NC, the roof gets anywhere from black to green. The only way I've found to adequately clean it is to spend a day on the roof with a bucket of Mr. Clean Magic Erasers and lots of elbow grease. I would NEVER consider using a pressure washer as it may penetrate joint seals and cause future leaks. I did find a Mr. Clean Magic Eraser mop that allowed me to stand up when scrubbing and it did a pretty good job. But there's nothing that get it as clean as good ole hands and knees scrubbing. The erasers make the scrubbing a little less intense than just using soap and a rag, but I won't lie to ya....it's still a job!

I would not use a pressure washer. (yes, I know some do...)
Can you see the roof from below? If not then just leave it alone.
Doesn't hurt it at all to be dirty.

out of sight, out of mind.