My WiFi status icon on 4.1 is grey, even when the connection is working fine. Why?
There is nothing wrong with it. Its the expected/correct behaviour of a freshly installed ROM that does not have Google Apps (gapps) installed. Thus, the telephony/wifi signal will show up as grey.
Its only when that Google Apps (gapps) are installed, then it will show up as blue, this is for ICS upwards.
In Gingerbread, if no gapps is installed, and there's wifi connectivity, its white, when gapps gets installed, it changes to the typical green that is known under Gingerbread.
To resolve this, please install the appropriate gapps suitable for your CM10 ROM.
Edit
I am under the impression that GTalk application and service is part of the GApps hence my comment below to Izzy about this...and seems to backup the fact that if gtalk service is not present, the signal colours do appear different.