There are plenty of Asians that have curly hair, including some Indonesians. From Fiji to Borneo to the Philippines there are certain ethnic groups that have curly hair and can grow what you would call an Afro. That said, Obama's childhood pictures do show hair that is more likely to be associated with blacks.
Having lived in Indonesia for two years, I do find his facial features to be similar to many Indonesians. Obama is definitely multi-racial. The only question in my mind is whether Obama Sr. was the real father.