"white" is a racist label that does not take into account the complexity of world history. It may be reasonable to use it in contexts of historical racism, e.g. in America (where many Slavic people were almost absent) or Sub-Saharan Africa (zero Slavic presence during colonial times), but it just does not make much sense elsewhere, e.g. it's absolutely irrelevant when describing ethnic tensions between Slavs and Caucasians or Central Asians.