NEVER be ashamed of your skin color when it comes to cosplaying. I have been at this hobby for over a decade and I am an African American, plus sized female. Two strikes against me when it comes to what this new, more mainstream society thinks of cosplayers. It has never detered me from cosplaying and I will never lighten my skin just to cosplay a certain character. Cosplay and costuming should always be about the actual costume. Is your wig on point? Costume ironed? No loose strings from your seams? Then you are good. But most importantly, are you having fun? Because this is about having FUN.
Skin color. Gender. Size. Age. Etc. None of these matter. The costume matters. Having fun matters.