I have a Scottish husband and can confirm that people here often warm to him instantly just because he is Scottish. I'm from continental Europe, and that's where we live, so I think I can also assure you that it has nothing to do with hostility against the English. They also like him more than me! It's just celticism. People romanticise the celtic cultures, the music, the whisky, the pubs, the kilts, the mythology, the plucky Braveheart-inspired reputation. When I tell people here that my husband is Scottish, they are very interested and there is often a note of envy because they're basically imagining Jamie from Outlander.😂
Generally we like the English just fine (and there are plenty of Anglophiles who love British humour, London, Harry Potter, English football etc), and certainly no less than other European nationalities! It's just that some people really, really love the Scottish and Irish. Nothing to get upset about or take personally.
If there is hostility, I cannot imagine it has anything to do with Britain's colonial past. Almost all western European countries were involved in that. We don't care because we're too busy fixing our own mess. Also, euroscepticism is everywhere now, not only do most people not care about Brexit, many actually admire it. If hostility exists, it might have something to do with the current cultural dominance of the English language. For example, English has become such an important language in science, tourism and business that lots of careers here are not open to you if you don't speak English well. English also dominates pop culture. People who have no gift for or interest in languages (and yes, they exist here too) may resent that. They feel like they should not have to speak English because they do not live in an English speaking country, but they simultaneously notice doors are closing to them because of their refusal/inability to learn. And because of this, they can be a bit hostile towards English speakers. As an English teacher here, and someone with many English speaking friends, I do occasionally encounter this attitude.