Smoke from tail pipe

I just got my catylatic converters change took it to
a smog shop passed everything but the visual
smoke test. My question is its has a small amount
of smoke coming out.  Not not large cloud of
smoke or enough to leave a smoke trail. Its light.
No milky white oil, no check engine light on. Drive
fine. But has been sitting for a year. Start it up
every week just so it doesn't die. Could the smoke
be from sitting to long and with new catylatic clean
the system out? The smoke is very light and cant
really tell if its white or blue
Its not black i know that much.