Other DAW’s are catching up with updates to counter this behaviour. REAPER has a great but small dev team, this (GUI) could not be a priority…. (it should be IMHO)Hoping to get an update regarding this issue. In the meantime: on 10.13.4 (17E199) low resolution mode could be a partial and temporary solution.
[REAPER HSierra Lowresolution - YouTube](
https://www.youtube.com/watch?v=GbaJuNeC17I)
[REAPER HSierra Lowresolution adjust mixer panel - YouTube]
https://www.youtube.com/watch?v=09tMWS4dQ5A
[REAPER HSierra Native RGB - YouTube](
https://www.youtube.com/watch?v=Q-K775FiygY)