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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- Judal (Magi: Labyrinth of Magic): 80% (Wig Overhaul) Katsucon 2017
- Galaxy Print Shiro (Voltron, Original Design): 78% (Arm Work) Katsucon 2017
- Blanche (Pokemon GO): 85% (Sewing) Katsucon 2017
- Yuuko Ichihara [Iris Yukata] (xxxHOLiC) : 91% (Wig Styling) Katsucon 2017