I’ve added the ColorComb based color picker to the AvalonStyleEditor add-in:
When you open the color picker dialog, a color under the caret is loaded as the current color. After you select a new color in the dialog it overwrites the old color in the style editor. You can open the color picker from the editor toolbar and with the Ctrl+P keyboard shortcut.
I’ve also added the toolbar to the style editor that is present both on the Style page and in the Tab Coloring Rule dialog:
Download link: AvalonStyleEditor v1.0.1.