Fix the default notification color in dark mode

In change Ib8840d04093094c324d8bdce5b2e84c93a94db8d I removed the dark mode color override of this color, but the light mode color was too dark to work correctly in dark mode.  Restoring the dark mode version of the dark mode color for all cases works fine.

Fixes: 190351384
Test: post two notifications into a group using the same color but different icon; observe that the 'grayed out' icon is visible in both light and dark theme.
Test: check shelf in dark mode; the 'more' dot should no longer be dark
Change-Id: I0b75c6b0da5e1c679ab962d826c2e6d2c3f742e9