I'm a current student. Glasgow uni is diverse, much more so than Strathclyde uni, more than a third of my science classes are made up of black, Asian and middle eastern students. I can confirm they have an afro Carribbean society, I've seen them at the black history month event they did 😀
There's lots of country societies around campus and in general there's loads of societies, honestly Glasgow uni is fab for societies and things to do.
Strathclyde uni has been more than 90% white from my experience of my sister going there. Glasgow Cally seems similarly undiverse though don't know anyone who goes there tbf. I think this is because Glasgow as a city in general isn't that diverse (though there are large asian and Chinese populations and it's much more diverse than Edinburgh) so because Cally and Strath are heavily commuter student biased and Glasgow uni has a more even mix of commuters and students moving to Glasgow that's why.