We need ColorInputField, which can be a part of FieldGroup. The value of this field should be an rgba string, for example "rgba(66,20,20,1)". The UI could be a square or circle filled with the color and gray text with rgba, which corresponds to the selected color.
When user clicks on the field, ColorPicker should come up. OK in the ColorPicker should sets the value of the field and change the fill color on display. Closing color picker without clicking OK, should not change the value of the field.