I'm building a mobile application and due to the data driven nature of the app, we ask users to enter their ethnicity. I was thinking about asking on the signup page, but perhaps this is not the right place to ask.

What is the standard list/selection method? Should it be single or multi-select? Also, does anyone know how to find a comprehensive list of ethnicities so nobody is left out? I've looked at various other websites but either this field isn't present or where it is the list is different.