I try to use three lineweights for reduced size prints (thin, medium, thick), and four to five lineweights for full-size prints (thin, medium-thin, medium thick, thick).
There isn't much organization for now, in the past it was almost like somebody threw a handful of darts at the color table but I've moved that forward a bit. For 3D models and derived elevation/plan drawings named colors (e.g. GREEN RED MAGENTA) for annotations and general lines, and numbered colors (e.g. 9 - 249) for 3D objects/object lines which all plot the same weight (different disciplines can choose pretty much any colors they want and still get the same result). Numbered colors 250 - 254 plot a progressive combination of half/quarter tone at thin/thick weight. For schematic type drawings (e.g. P&IDs) its named colors for everything.
Trying to group colors gets a little difficult, as the colors at the outside edges are too dark for common use plus many of the colors are too close together to pick out differences. The way I figure it there's around a dozen "unique" colors that can be pulled out of the numbered colors area if you don't duplicate the ACI hard-equivalent of the named colors.
I'm slowly walking everybody towards a few basic concepts e.g. text being a separate color from lines, colors from the same grouping behaving in similar ways, etc. Due to tight scheduling, multiple projects having different schedules, and different supervisors wanting different things making *any* changes is like herding cats through a catnip farm.
