Plotting question??

I'm doing structural drawing. I inserted some architectural lines for
reference and I want them to be plotted in grey or lither mode. I go into
ctb file and I change the screening for particular colour. All arch lines
and solids are plotted lighter but they jump on foreground, so other lines
which should be darker are wiped out when intersect with lighter lines.
I hope you understand what I'm talking about
How to fix it?
thanks