You mean the pistils are turning brown? That's completely natural and what happens the closer to harvest you get! When about 50% of them turn brown, you should start looking at the trichomes to see how THEY are doing... they'll start off clear, then turn milky, then turn amber.... you'll want to harvest when about 10-20% of the trichs are amber.
Good luck and enjoy the final steps of your grow! It looks GREAT!