SET_WP_DEFAULT_BACK_BORDER_COLOR sets the default back border color of new workplanes.
-->(SET_WP_DEFAULT_BACK_BORDER_COLOR)----|GET_RGB_COLOR|---->
SET_WP_DEFAULT_BACK_BORDER_COLOR :HSL 0.5,0.3,0.7
Alternatively, you can use the HSL and RGB sliders on the color menu to specify the default part color.