Any opening will cause a chimney effect, drawing air up and into the attic.
This will carry dust, construction smoke and moisture up with it. Possibly,
gas or oil heaters were installed if the temperature dropped and caused
smoke soot to carry up and into the insulation. It is one of two things,
either dust and/or dirt OR it is mould caused by water or dampness.
Insulation does not rot (possibly cellulose would, but not in that short
time). Normally all cracks or breaks in the vapor barrier will have a dirty
stain in the insulation right behind the opening. If the speaker holes have
been left open they are ripe for the dirt to be carried into the insulation,
especially from the construction activities.

"Mike" wrote in message
oups.com...
Several weeks ago a contractor building an addition on my home
installed R-30 insulation in an attic space, right above a ceiling.
The ceiling has now been sheetrocked but I can still see the insulation
in some holes cut for speakers and in the ceiling of an unfinished
untility closet.

The original color of the insulation was bright yelllow.

Above the speaker holes the insulation is now solid black. And in the
ceiling of the utility closet, behind a plastic moisture barrier that
is stapled to the bottom of trusses, the insulation is streaked with
black.

Is this right? Why would the yellow insulation turn black?

mh