I agree with Ichigo-- those characters have two totally different colours, and unless you dye the wig, I don't think one is going to work for both.
Going to con with only one cosplay can actually be a lot of fun, though! If you're really not up for that, though, you could always pick a cosplay that would make use of your natural hair.
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- Emperor Lelouch (Code Geass): ??% (Patterning) Katsucon 2017
- Female Kamui (Fire Emblem): 2% (Planning) MAGfest 2017
- Pyrrha Nikos (RWBY) Ver2: 56% (Weapon Work) Otakon 2016
- Honoka Kousaka [jester] (Love Live!): 10% (Planning) Otakon 2016