No, the ablative material is white (like on the center core). The darker fins are the fancy new titanium fins (note they're a little larger too).
Not sure why they went with the new fins on the side cores and not the center core... The side cores are going to have a pretty tame reentry (gentler than a Falcon 9 to LEO), while the center core will be coming in very hot. Currently they only use the titanium fins on very hot GTO reentries.
On the SpaceX subreddit, I've seen a few mention that it's probably because of the different aerodynamics with a nose cone; they need more control authority in that case.
