when i ruptured the membraines i did not know it was anything other than urine at first because the colour was clear. so didnt have any tinge to it.
But when it started happening at irregular times i took more notice.
The smell was what made me concerned, it had a really distinctive smell. Kind of sweet, not a nice sweet though! you could even compare (sorry if tmi) to the smell of sperm....
i think once you loose the plug/ have your show maybe the fluid chances somewhat.