The voice cast trailer gave fans their first glimpse of FemShep in action, however, this isn't our default FemShep.
Bioware Edmonton’s Community Manager, Jessica Merizan has gotten in touch regarding this matter. “There are two options on the character creation screen “Default” and “Custom”. I believe that the brunette Shepard you are describing is one of several “custom” options that you can then edit. The “Default” Shepard is the redhead you see in the trailer. She is not customizable (similar to Dragon Age II or how the male Shepard option has been in the past).”