I started cosplaying as Cortana back in 2005, and finally last year I completed the trio with Halo 3 Cortana
Each is its own costume, I did not re-use the suits for any of them. Halo, then Halo 3 in the center and Halo 2 on the end. The center costume was painted by airbrush and the other two were both done with fabric paint. As for the face make up that has also changed with the costumes. Halo was done with Mehron Hyper-Formance CreamBlend in purple. Halo 2 was done with a mix of Ben Nye Creme Colors and MagiCake Aqua Paint. As for Halo 3 that was the easy one, I just had my Dad airbrush my face LOL Each time I wore the costumes I made sure to use black eye liner as well as false lashes as to not "loose" my eyes in photos. I always stood by my color choices for the costumes although most people will argue with me on it. First game purple, second game lighter shade of purple and third game blue. If I had to pick a favorite it would have to be Halo 2; since I got to wear it on stage for Video Games Live last year at ComicCon.