Sorry if this seems like a controversial topic, but I've seen this discussion show up in a few places and people supporting two different sides of an argument without actually sourcing anything factual.
With respect to B&ME representation within the Dunkirk pocket, I've written about it here, and given more context here. In the Dunkirk pocket, there was not inconsiderable representation from French colonial troops, with elements of ten colonial regiments being trapped in the pocket. Some of these troops would share ships with British troops, while one of these regiments was one of the last ones holding the pocket open. The British Army, meanwhile, was not segregated, and black men (either from Britain's small Afro-Caribbean population, or from Caribbean and African nations who travelled to the UK to join the Army) could and did fight in it. While there's little evidence for such a presence at Dunkirk, this doesn't mean they weren't there. There were also four companies of mule drivers from the Indian Army in the pocket. The Merchant Navy, which provided crews to many of the ships taking part in the evacuation, had 50,000 sailors from Africa, China and India, compared to 132,000 British sailors.
Just a reminder for those interested in not only this, but other aspects of accuracy from the film, make sure to check out the Dunkirk Megathread we had last week which collects many of them together.
Edit: Also, if you are interested in discussing the film, this isn't the place. But there is a whole subreddit, /r/Dunkirk, to share your thoughts on how awesome (or snooze-tastic) you found it to be.
Just a follow up question since this seems to have been asked quite a bit recently:
Do we have any images of soldiers in the pocket that were "minority" soldiers, if you will? I know it wasn't a time for a lot of casual photography but I suspect there are still a lot of photographs from that episode.