Re Donna R. Cubberly's "product available that could be used to fill
in the smal gaps created by butt-joining western red cedar crown
molding around the ceiling of a living room"

The traditional trick is to not cut the molding square butted, but
lapped on a 45 degree angle, and nailed thru the lap.  Even if the
joint opens up a bit you don't see a dark gap through the pieces.
Outside corners are customarily miter cut, inside corners coped, not
miter cut (that's the tricky part because you often have to undercut
the coped piece without disturbing the coped line.  I've used this
technique on wood and in cutting pressed metal moldings around "tin"
ceilings, and with neat work, looks pretty good even after quite a
few years of settling in.  As for blending with western red cedar,
you may have to stain up your own filler, experimenting until you get
a decent match.

Tell us how it comes out.

Rev. Jim