"murky subject" is correct and usable in written English.
It is typically used to refer to a subject which is difficult to understand or explain. For example, "The professor discussed the murky subject of psychological conditioning theory."
But that is no excuse for frightening everybody, nor for making an already murky subject much murkier.
Young punks Iceage have caused a stir recently with thrilling live shows and critically acclaimed records, yet there is one murky subject that just won't go away.
For the sake of partisan controversy and ratings, the news media seek photogenic people who are then introduced as "China experts" and become identified in the mind of the public as shedding clear light on a murky subject.
And then, imminent global apocalypse aside, we can quietly give thanks to the Russians for ensuring, whatever their true motives, that a murky subject is being dragged closer to the light of proper scrutiny.
The murky subject of who can and cannot advertise could be further complicated by a recent Supreme Court decision on corporate political speech.
Remember, history is a murky subject filled with endless debate, and the same rule applies when it comes to wieners, baby cannons, and poopers and junk.
The murky subjects of toxic debt, trading in oil, the economy of housing, Brexit and how to count your bitcoins are made more comprehensible thanks to NPR's Planet Money.
At home, his life story is murky and subject to wild rumors.
The relationship between Mr. Heywood and one of China's most fabled political families remains murky, the subject of considerable gossip and innuendo.
What happened next is murky, and the subject of the books and lawsuits.
And even the murky designations are subject to inflation: as the Times has reported, it is the Administration's practice to assume that any adult man in the vicinity of a strike can be called a militant.
