25 year old redwood fence, never cleaned or stained, and pretty much matched the shake shingles on the house. Simple water & bleach mix ( 20-25% )bleach in Hudson sprayer. It was a hot summer day so I'd saturate 8-10 boards followed by pressure washer, repeat until done.
The lighter color about a third the way up is natural bleaching from the sprinklers.
Forgot to add don't use cheap store brand generic bleach.
Clorox is your friend.