The colour of all the lines that are shown in section are all controlled by the cut line pen in the 'frame and sash' tab as shown in my image. This is also the pen of the frames in plan. You would think that the 3d pen (light blue) would have some affect on the uncut parts in section, but it doesn't for some reason!
If these settings don't seem to change anything, make sure you have 'Enable Objects Attributes' ticked under cut surfaces.
If you have any doubts as to what a particular pen or fill controls, try setting it to a unique colour and/or fill and then look at the element in plan, section and 3d to see what has changed.
Hope that helps.
Rubia Torres
