Hi,
difficult question: let's say you have a blue candle, blue is water but the candle, however, represents fire, if you put it into the north area and light it, you'll burn your career.
If your furniture still looks like wooden furniture despite the color, then I'd say it's wood.
From my own experience, I would not be too strict on that. If you have one object representing each element then it should be enough. If you have much wood, place a fire object to balance it. One item usually is enough I think you don't have to have the same number of objects of each element in a room to have balance.
Love,
Astrid
