In recent months I have had an endless series of emails from folks experiencing issues with monitor (display) ICC profiles. Usually the visual result is obvious banding.
Recently, there are a number of reports around that macOS 10.14.6 is breaking monitor ICC profiles in a number of contexts.
Specifically the issue arises if the profile in question has a Tone Response Curve tag ('curv' tag) encoded as 'simple gamma', rather than a table. Most monitor profile making software (such as i1Profiler) - apparently generates a table, so many will be ok. But many others won't - notably those using monitors with direct hardware calibration (such as NEC Spectraview, BenQ Palette Master, Eizo ColorNavigator etc) may experience issues.
If you're using the in built OS profiles, such as Generic RGB or Adobe RGB, with a monitor for any reason, those will be broken too.
One imagines a fix will be forthcoming soon, but if you're using colour management on a Mac, disabling updates for a bit might be a good idea (or rolling this update back if you have already installed it). If you're interested/affected, the Colorsync mailing list has an ongoing discussion (Aug 2019 Archive).
(See also our cautionary advice on macOS X Catalina).
And if you're using Windows, V1903 had issues too (now solved though).