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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- Mermaid Ariel- Swimmable (Disney's The Little Mermaid): 23% (Patterning!) Colossalcon 2015
- Magic Armor Link 2.0 (LoZ: Twilight Princess): 50% (Armor Revamp) Spring 2015
- Genderbend Makoto (Free! Eternal Summer): 27% (Wig Styling) Colossalcon 2015
- Emperor Lelouch (Code Geass): 2% (Planning) Spring 2015