It has a benefit per Pat Symonds:
Q: Redbull has painted their car in matte paint. Is there any aerodynamic benefit to that paint.
A: And they are the second team to do that, aren't they? The first one of course you know is Williams.
Q: What is the thinking behind that?
A: The surface finish on certain parts of the vehicle are very important. The requirements are different in different parts of the vehicle but...yeah,,,there is something there.
Starting at 29 minutes: http://www.motorsportmagazine.com/multi ... -podcasts/
I suppose it could be misdirection but from the conversation I am inclined to take it at face value.