سیم+آب
سیم= silver
سیماب=جیوه=mercury

--------------------------------------------------
Note added at 2 days2 hrs (2013-04-25 21:24:22 GMT)
--------------------------------------------------

I suppose مفتول here means a "thread" or "fiber", according to Loghat Nameh Dehkhoda (the persian dictionary).
It means some rich women wear burqas which are decorated with strings or threads whose colour is like silver or mercury.

--------------------------------------------------
Note added at 2 days2 hrs (2013-04-25 21:25:06 GMT)
--------------------------------------------------

I suppose مفتول here means a "thread" or "fiber", according to Loghat Nameh Dehkhoda (the persian dictionary).
It means some rich women wear burqas which are decorated with strings or threads whose colour is like silver or mercury.

--------------------------------------------------
Note added at 2 days3 hrs (2013-04-25 22:54:28 GMT)
--------------------------------------------------

No. مفتولی is not related to hair but related to some ornamental threads or strings sewn on the burqa. Now the colour of this thread (مفتول) is like silver or like mercury.
مفتول + «ی» نکره = a thread

--------------------------------------------------
Note added at 3 days16 hrs (2013-04-27 11:22:13 GMT) Post-grading
--------------------------------------------------

No, it does not denotatively refer to the metal "silver". It refers to "mercury". Since silver and mercury have the same colour, this name (سیماب) has been assigned to mercury in Persian.
In your sentence, the colour is meant by the original writer.