One of the center caps on my '10 was discolored while it was still sitting on the lot. I had them replace it before I took delivery. Several months later, they are all starting to take on a slightly blotchy/yellowed/milky appearance. No chemicals other than car wash and water ever come into contact with any part of the wheels (i.e., no tire shine).
2 of mine were blotchy the other 2 where nice and shiny, so I originally thought some wise ass at the shop popped them off and replaced them with older ones. But, don't think so now that I hear others are having the same problem. I ordered new ones, only about 6 bucks each, and put a good coat of wax on them before installing, we'll see how these hold up.
Looks like inferior quality coating over the aluminum that isn't holding up to moisture and/or UV. May also be contamination of the aluminum before it is coated since it appears to be under the clear coat instead of on the surface. I had a similar problem with virtually identical center caps (without the "H") 18 years ago on my '92 Grand Am.
The '06 Ridgeline had plastic caps with a molded "H" before they changed to aluminum with a painted "H" in '07 (cost savings at work I'm sure).