C.C.
I'm a first generation Asian-American and can tell you that the stereotyping you witnessed is common & unfortunate. First, as your child grows, teach her what you can about her birth culture, but your daughter isn't Asian, she's Asian-American. Also be sure to teach her about your family's history & culture. With regard to overt racial comments... ignore them. You have every right to be in that public place, and leaving just taught that uneducated individual that his opinion made a difference to you (and probably made him feel justified in saying it). With regard to how to address it with your child? A simple way my mom explained people of different races & colors was to take me out to her garden & show me all the different pretty flowers. it takes flowers of all different colors, shapes & sizes to make a beautiful garden.
I want to advise you now, I was sometimes caught off-guard by racial stereotyping in the most unexpected places. Usually it was well-meaning people who would ask me "What nationality are you?" or "Are you Korean?" I used to be offended, given that I don't walk up to the average caucasian person & ask them what nationality they are... but you get used to it. My personal favorite was being complimented on how well I speak English. (I would hope I speak English well, given it is the only language I speak fluently.) And tell her never to date boys who have a "thing" for dating Asian girls. That's just plain creepy.
I won't lie, your daughter will be hurt by this now and again, but she will also learn to love her identity. She will love her shiny black hair & her smooth porcelain skin. I look at how my mom has barely aged in her 70 years & am grateful to know how I might look 30 years from now.
Please, teach her to love who she is because of the beautiful person she is, inside and out. Teach her to smile when people ask what nationality she is and teach her to reply "I'm American, silly! But my parents chose me from _____"
(Oh, and teach her that she'll look ridiculous with blonde hair, but let her find out for herself if she must. I think we've all done that at least once.)
Best of luck & much love,
C.