[ChisaChi]

From my brief experience in Japan, I'd say any form of racism I might have encountered would have been so passive that I didn't recognise it O_o. I'm half Burmese (so olive skinned), two of my group were of Chinese descent and two were of British descent. The white boy was declared 'cute' everywhere we went; the two of Chinese descent got some curious questions but always friendly; and I just got the occasional 'jyouzu!' for my lame Japanese XD

I imagine you'll be met with some curiousity for being a foreigner and looking different from the stereotypical American, but I doubt you'll encounter any overt racism.