That's the color of pressure treated lumber out here. I don't know what they treat it with but it looks totally different from whatever they used back on the east coast.You're lucky that you can use 4x4's for posts there. Where I'm at, even 4x6's will twist and bend after a few months. Most of the nicer fences in my area are built out of 6x6's or galvanized pipe. I've also never seen posts that shade of brown. I don't even know what that is!!!!
I did a fence five years ago at my other house and it still looks new... a little bit of aging of the fence wood but it was untreated and unprotected. The posts were the same 4x4 treated and so far no issues. Yeah things are different in San Diego.