Just one advice: stick to old centers of towns and you'll be ok. I'd not take my African friends to the suburbs in Eastern/Central Europe. But that's all.
Yeah - black people are not so unusual here in Budapest, downtown, and the high-rise suburbs are probably hostile, but you wouldnt go there anyway.
Just if you'd venture into more outerlying countries - Romania, the Baltic states - you might have some more out-of-the-ordinary receptions. Antillean colleague of mine went on a church trip to those countries and was gawked at quite a bit, in both positive and negative ways. That was a while ago, admittedly, but yeah, country like Romania is a very different from Hungary.
(Then again I met a black guy here once who went clubbing in Belgrade every month or so, because the parties there are wilder, and he was very enthusiastic..).
I wouldnt even think of going to Russia, if I were black ... lots of unpleasantries happening there to people of colour.