Chains and casette are rusty
A great rule of thumb is "Dry lube for dry conditions, wet lube for wet conditions". 

A bit of surface rust on an otherwise well maintained cassette and chain is only a cosmetic problem. If this is a concern, clean the chain, lube with a wet lube, wipe dry. The trick is to 'over lube' the chain and then wipe off the excess. I might be tempted to leave wiping the chain for a day or two to let the lube migrate around the links. 

As far as the cassette, give it a light spray of WD40 after cleaning. Don't get too much on the chain as its not a lube and you don't want it displacing the lube you just put on.