I meant only to illustrate how the comment I quoted in my original post showed a North America centric perspective, missing the point that the discussion was about online interaction among people from different nations, not different ethnicities in a North American country.

You are right that perceived ethnicity and actual ethnicity are not always the same in Europe, and that people do get treated differently because of the color of their skin. Discussing this is valid, but it was not valid or relevant in that particular discussion.

By melting pot society, I meant that many people whose families have lived for generations in that society have only a vague idea of where their ancestors were from before they immigrated, and they consider their own ethnicity to be one of the macro "ethnicities". Ethnic markers are not so much less visible (though that too), as society in general ignores them and dismisses them as irrelevant. Many Americans who have preserved their ethnic identity find this constant dismissal of it very hurtful.