Have you ever seen pictures of Kimora Lee- Simmons? She was a famous model in her time and is the former wife of Russel Simmons. If you have not heard of her or seen her picture, her mom was Japanese and her dad was black. Her skin tone is similar to that of a black/ white mix, but she has 'asian' eyes. Imagine Hally Berry's skin with the hair and eyes of Lucy Lu. I personally think its a beautiful mix.
If your friend wants to see a black/asian mix personally, I would recommend her taking a vacation to Jamaica. I took a vacation there recently, and met many people who refered to themselfes as 'blackinese' (half chinese, half black). Unfortunately, I havent met any mixed black/ asian where I grew up, hence my suggestion to travel, but maybe it is possible to find such a person nearby in your area.
It is possible that your friend might be worried about the stigmitization of the child. Personally, I am a white girl living in Korea, and there are a few mixed races here (black/ korean, white/korean, etc). However, these children are cast aside (with the exception of a famous mix race actor) because of the prominent Confucianism thinking here. I find that americans a more tolerant of mix children (as much as I like the people here). Just point out to your friend that if she does decide to marry this guy, that all that matters is her children being loved, not just how they look.
I am mostly concerned, though, that your friends hesitation is a clue to deeper problems under the surface. If I met the man of my dreams, my first thought would not be the looks of our children, regarless of what race he was. I would recommend seeing if it is in fact, something deeper.
Good luck!