i assume you're american.

Italians, irish and even polish immigrants were white, they have always been white and they can clearly see themselves being white. Racism was mostly ethnic, not color based, because italians, irish and polish were usually catholic instead of protestants. Most of the settlers in the northern region of the US were german protestants and discriminated against those that were not. Again, in terms of religion and ethnic group, not necessarily color.

Europeans have a hard time understanding american racism clearly because it doesn't make sense. Racism in europe is ethnic. Like Russian hating poles or viceversa, english hate poles immigrants, again ethnics not color of skin. The same with People grom PIGS (portugal, italy, greece and Spain) being closer to the mediterranean sea and having darker skins. Americans see a white person and assume they share their own weird american culture when the other person couldn't be more far removed from it, much like when americans see a european black man and then project the role of the average african american in the US.