What colour are US mail boxes?

I think that the generic answer is red. However, I found this informative: Some people choose to have their mailboxes the same color as their house, or at least compliment the color of their house, while to others it doesn't make any difference. Some people have their mailboxes painted like an animal. Some people choose a neutral color mailbox and decorate them for the different seasons.

http://www.streetdirectory.com/travel_guide/30947/home_accessories/choosing_a_mailbox_in_the_united_states.html

If you mean what colour are the post boxes on street corners where someone can post a letter then all I seem to see are blue
https://about.usps.com/who-we-are/postal-history/collection-box-colors.pdf

They have changed colour every few decades, the current design began in 1993 (satguru).

Here's a photo of a U.S. Government mailbox for those of us who are sending:

http://www.freefoto.com/images/04/30/04_30_63---US-Mail-Box_web.jpg

For receiving mail, see BRY2K's post.