we are going to the Riu Palace Mexico this July, is there any nude beach or cloth optional area?

Brutas,

Check out this page:
Baring It All in the Mayan Riviera - Going Topless

Brutus, my wife and I are going to Cancun in October. How was your trip in July? Any recommendations for C/O beaches?

Here's an alternative for nude beach. Eden Bay resort in Dominican Republic. Not only it offers nude beach, the entire property is clothing optional, and it's an all-inclusive resort. Each accommodation at Eden Bay is individually owned. Go to www.nudist-rentals.com to see what's available for sale there.

This is considered a "family" resort
For clothing optional look at Desire.