It's a common myth that classical marble statues were pure white and boring. In fact it's modern consensus that they were very often skilfully painted, but the colours were lost to time.
Augustus looking very fine there.
Source (in Spanish): http://rodrigorivas3d.blogspot.com/2014/05/policromia-en-la-antiguedad.html
It makes sense they were painted. They painted everything else why not the statues?