Brown. like in rotting? Are just the hairs brown? How old are the plants? Are the buds squishy? Can you give us a little better description of what is going on? And tell us more about your grow. Are these inside or out?
First of all welcome to MP and your plant looks nice on the whole. I have no idea what that is. I first thought pollinated. Like DFN suggested, look under those red hairs and see what is under there. Look for mold I guess. Maybe pull those two off the plant and do an autopsy on the buds and see what you can find. Sorry I am not more help.
IMO, this is not normal. While there may be some reddening or browning of the buds, this usually happens far later in flowering than 4 weeks.
Can you tell us more about your grow, particularly your ventilation system? Even though the buds are still small, it does look like it could be the beginning of bud rot. You really need to check the brown parts to determine if it is bud rot or something else.