I'm not sure that they are painted but it looks like they are. What are they for?
Aviation Stack Exchange is a question and answer site for aircraft pilots, mechanics, and enthusiasts. It only takes a minute to sign up.Sign up to join this community
— airliners.net; cropped
In the photo above (taken in 2011, four years before the Pearl 15 first ran), that feature can also be seen; that engine is in the same family that includes the Pearl 15, the BR700 family.
— flickr.com; click image for a closer look
In the high-resolution Pearl 15 photo above, that feature is seen to protrude slightly above the blade's surface as if it's glued on. The location, protrusion, length, and being attached by high-strength epoxy, match an invention for fan blade boundary layer control by Rolls Royce Deutschland (the makers of the BR700 family):
Here, a feature (90) has been located on the high-speed (low-pressure) side (52) of a turbofan fan blade (40). The feature (90) is located toward the leading edge (55) of the fan blade (40) and extends from the tip (43) of the blade, inward. In this application, the feature is constituted by grit bonded to the blade using a high strength epoxy.
— U.S. Patent No. 7,878,759. 1 Feb. 2011. [Filed in 2004.]
Also, there is a possibility that device above can also be used for a new vibration monitoring and control system, wherein the device is made to be magnetically detectable, which is something R-R have mentioned very briefly in a press release:
... new-generation Engine Health Monitoring System that introduces advanced vibration detection ...
This is based on a newer (2015) R-R patent.