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): 59% (Styling Wig) Otakon 2016
- Dancer Marinette (Miraculous Ladybug AU): 74% (Styling Wig) Otakon 2016
- Misc. Revamps (Various): 0% (Planning) Otakon 2016
- Ariel Sail Dress (Disney's Little Mermaid): ??% (Patterning) Summer 2016