This is regarding a custom color picker on par with Windows and the Web interface which is integrated into the app.
Currently, Evernote uses the default system Mac color picker in a separate palette as you've shown. The hope is this, along with other inconsistent cross platform ui decisions could be consolidated. As an example, here is the color picker used for this forum (just shown as an example)
FYI: this thread was started in 2015 was following up on another archived post here from 2012: