Sikhs don't believe in color, creed, caste or race. You don't have to be a Punjabi to be a Sikh. You don't have to be Indian to be a Sikh. You just have to be a human being to be a Sikh. Be a part of the human race, that's it. A black person and a white person can definitely merge with the Creator. There are many mystics from Christianity and Islam, whom we have accepted as great beings. The best example of this is the fact that Sri Guru Granth Sahib Ji contains writings of people who weren't Sikhs, such as Bhagat Kabir Ji and Bhagat Fareed Ji. So Guru Ji (Enlightener) has given them the highest status. For Sikhs, when they bow down to Sri Guru Granth Sahib Ji, they bow down to the writings of those people as well. Why? Because those writings are concurrent with Guru's writings. Those people from other faiths have realized the Truth. The eternal true reality exists everywhere. People can access that reality and they write about it. Those writings are going to be enlightened writings. Enlightenment is not something that only Sikhs have. Everybody has it. 

You can watch Bhai Jagraj Singh explain this in the video below: