Cannot edit a copy of the ColorPicker Style in Blend. Also, cannot edit the Additional ColorButtonStyle. As a workaround use an implicit style approach. You can have folder with your XAML files and edit the Style of RadColorPicker in them. http://docs.telerik.com/devtools/wpf/styling-and-appearance/styling-apperance-implicit-styles-overview
Original title: "RadColorPicker should have a built in custom colour selector" I'm aware that I can add a custom colour selector to the RadColorPicker myself and an example is given in the Telerik WPF demos, but rather than having to implement this myself, I'd really expect this to be built in so I could just set a ShowCustomColors="True" flag and it'd be done. Other UI control vendors I have worked with have supported this functionality without making me do so much work.
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.