Currently, the text is very light gray which makes it hard to read. Think it should be black.
Agreed. The color of the text is #AAAAAA. On a white background it doesn't pass WCAG AA compliance. Contrast ratio is far too low. See this screenshot taken from snook.ca
It'll be much better at #545454 or even darker:
I've looked over a bunch of other StackExchange sites and none of the ones I checked have such a feint colour for the search field text.
This has been fixed on dev server. The change will be on live after our next production build(within 24hours).