Hi!
Day 12 brings us a Nightwing costume with red highlights.
"The red is believed to be a nod to the Bat Family, as most members of the Bat Family have used red in their costume in some way. His use of red is believed to symbolize his reunification with his mentor, his reconciliation with his past, and his willingness to be included as a member of the Bat Family."
from 10 Things about Nightwing
Seems a bit deep but hey there's gotta be some reasoning behind it right?
Enjoy!
Rob