This subject is likely to cause a heated debate, or even a flame-war, whenever it is brought up on forums, so I’m going to be very precise with my wording here.
No matter what colour your skin, what ethnic group you identify with, or what race or nationality you are – you can cosplay as any character you want.
That’s it. It really is that simple.
Now an important point to remember:
For various cultural reasons, mainstream media in Japan, America and Europe mostly feature lighter-skinned characters. As a result anyone with darker skin will find the characters they share characteristics with are very limited. Don’t let this stop you – cosplay who you want. If you want to be an African-American Sailor Venus, an Indonesian Hatsune Miku, or any kind of non-white Guy or Rock Lee, you’ll be in excellent company!
Sailor Venus – Chaka Cumberbatch looking fabulous!
Hatsune Miku – Ikara brilliantly adapted Miku’s style to adhere to her faith’s requirements
Guy/Rock Lee – source unknown, but don’t they look amazing?