I would like to put a concrete floor in my living room its on the first floor with only a small crawl space under it. It has a plywood subfloor that I would like to cover with a thin but durable layer of concrete that I can stamp and color.

As long as its not too thick, you should be fine, Do you have a basement?

The Thickness Will Be A Problem, It Needs To Be Thick Enough To Stamp And Also Thick Enough To Not Crack, I Really Doubt You Joist Will Hold This Weight, All I Can Advise Is To Lay Durock And Use Some Natural Stone,or Some Type Of Tile Like Slate To Get The Look Your After.

One Thing To Keep In Mind The Plywood Floor Moves Cause Its Wood This Could Cause Your Floor To Crack If You Tried To Pour A Slap That's To Thin,