English has between 16 and 22 vowels (iirc) depending on the variety. English speakers that use a different set of vowels than each other often cannot understand each other at all at speed.

Color and colour are different pictures of the same word.

Ask people how many different vowels there are in this set of words: trap, bath, palm, lot, cloth, thought. Most English speakers will make out two-four vowels from those 6 words. But they won't agree on which words share the same vowels.

There are other phonological differences between English dialects, but for the most part you can notate them as sounds that merely some dialects don't distinguish (e.g., nonrhotic dialects dropping the `r' sound).

That's not a pronunciation difference though. Almost all english dialects and regional accents pronounce that word very similarly. It's just an introduced spelling difference for aesthetics.