(*Also see this issue in Designer Beta.)
Looks ragged in both Color Studio and context pop-overs as shown. Changes under Preferences > Performance > Display have no affect.
2013 iMac -- non-retina, Mojave 10.14.1
In addition to the already noted …
Wacom Intuos 4, Driver 6.3.16-12 (and last few versions): Pen side switches don’t behave as expected.
Using Affinity Designer 1.4.1, seeing same issue in latest 1.4.2 beta.