This feature should include:
1. When focused, pressing down arrow key should open the picker, like in WORD's color picker
2. Automatic button should go into keyboard focused state when down arrow is pressed and the focus is in the split button.
3.Arrow keys should move the focus to colors in the pallete views. Space/Enter should select the current color.
Feature is mixture of Keyboard logic, new Focus states in PalleteViewItems, PalleteView, ColorSelector, ColorPicker.
Like in Ribbon (when keyboard navigation was implemented) some controls might need additional keyboard focused states.