As someone who lives near Evanston and also spent 3 years delivering food TO Evanston, I learned the basic boundaries of the suburb.
I made this lil' map here to help you out.
NO = These areas are dangerous and crime filled or just plain undesirable, so I would highly recommend you avoid these parts.
MEH = Decent neighborhoods, but can be gritty in certain parts. Not as bad as the "NO" neighborhoods. Contains more affordable housing.
OK = Good area, not as good as the "nice", but probably slightly more affordable. It's "Okay", basically.
NICE = Beautiful suburban feel, nice clean homes, safe, but is pricey.
Hope this helps.
As for being an interracial couple - you shouldn't have to worry about it at all. Despite what some people may say, Evanston is a very liberal suburb and I don't see you having any trouble with your relationship.