3 Different colors for the basic "background curves" depending of the 3 axes?
like in this crazzy nurbs car's tut
http://www.etereaestudios.com/docs_html/nixus_htm/nixus_makingof_mp01.htm
(you can clic on the little up white triangle for more images :)
He uses directly curves and surfaces as "3D sketch" for research design !

another crazzy nurbs car tut by the same guy
http://www.etereaestudios.com/training_img/sentinel_tutorial/sentinel_tutorial.htm

Ps Little question
How use the "Circle tangent tool" for have a circle tangent between the "big rectangle" and the "big circle" and touching 2 precise points?
(the center of the little circles) ?
(because when a point is yet drawing on a curve, this point can'be choosed as first point of a curve of the tangent tool :)

If exist of course, seems not in this case of the little circles, but in the general way?
Like the 2 points (center of the little rectangles)
This last one exist
( I have drawing the circle tangent first and draw the little rectangle by centers after (curve "on" + intersection) , erased the circle :)

Or I must read a geometry's manual for construction of particular figures :)