I assume you're talking about either the Marine Greens Or the Dress Blues. You can wear the Blue Dress Uniform for occasions. But I need to know which one you're talking about specifically.

The is a dress blue Marine Corp uniform and is worn by someone who no longer in active duty, is that permitted?

You can sill wear it, Its the pride of the UnitedStatesMarineCorps, when ever you vivist somewhere in washington like the USMC war memorial, its an honor for you to visit it with the Dress Uniform.

The answer to your question is no. A former Marine (not a retiree) must have served during a time of war (i.e. earned the National Defense Medal during your time in service) and received an honorable discharge to wear the uniform. They are restricted to wearing it to military funerals, memorial services, weddings, inaugurals,parades on national or state holidays; or other parades or ceremonies of a patriotic character in which any active or reserve United States military unit are taking part. Recipients of the Medal of Honor may wear the Marine Corps uniforms at their pleasure except for those specific occasions listed in paragraph 11002 of the Uniform Regulations. A retiree/reservist can wear the uniform for basically any event in which they wore the uniform while on active duty. More importantly, anyone who wears the Marine Corps Uniform must abide by the Marine Corps Grooming standards to include abiding by the height and weight standards (paragraph 8000.2 of the Uniform Regulations). On a sidenote, nothing says phony vet or phony hero more than a sloppy looking dude wearing a mish mash of military uniform parts & patches with rank insignia and medals that he didn't earn. For more detail on your question, see the following official USMC page: http://tinyurl.com/ydmprg

An active Marine who is not currently working cannot wear a uniform either. For example, a Marine cannot go to the grocery store or walk around a fair in a uniform. A Marine should change into his attire while at work and out when leaving.

Yes, they can, but they shouldn't only because it looks stupid. They're also likely to suffer some mild harassment from current Marines.