With the introduction of brush assets, there are now two reasons that
motivate turning this setting on by default.
* More paint brushes - Previously, there was a single paint brush in
Sculpt mode, this made the setting for general usage less needed when
compared to the 10 brushes that are now included in the essentials
pack
* Brush settings are lost on reload - Unless the changes to a brush are
saved to the asset as a default, the color for a brush is now no
longer persisted between Blender sessions. It makes little sense to
save a specific color for a specific brush on the asset level unless
it is needed for the brush functionality.
This commit ensures that the appropriate Scene flag is set for the
unified color and defines the default primary and secondary colors as
000000 and FFFFFF, respectively.
Pull Request: https://projects.blender.org/blender/blender/pulls/129127