There's a new build of ArtRage 6.0.6 with the following bug fixes:
Reference image crash on MacOSX using Retina resolution for certain reference images.
Ink pen going to 100% on MacOSX using Retina resolution if Ink Pen stylus property for Wacom Airbrush pen finger wheel associated with tool size.
Guide text size increased on MacOSX using Retina resolution.
Retina flag persistency not persisting correctly on MacOSX
Colour picker rendering and picking incorrect on MacOSX using Retina resolution.

See? I do love Apple users!