From what I've read in Prisoners of War and Their Captors in World War II ed. by Moore and Fedorowich, large numbers of French colonial troops, namely Senegalese and North African Arabs, fought in the Battle of France. Many were subsequently captured by the Germans with large numbers being shot, (up to 500 in Erquinvillers mid 1940 alone). Did these colonial troops have a large presence on the beach? Or were they predominantly relegated to guard the rear, and if so would that explain why so many were captured?
I wrote about this here. The French Colonial units were, for the most part, the last troops in the rearguard; that said, the confusion of the beachhead meant that units frequently intermingled, and it certainly wouldn't be implausible to see them there. There were few British colonial units at Dunkirk - just four companies of Indian mule drivers. These were evacuated over the beachhead. British units were not segregated, and could include members of the admittedly small British non-white community (or West Indians who travelled to the UK to join up). Many of the ships taking troops off the beachhead had crews from the Merchant Navy, which recruited widely from India, China and the British African colonies.
After a quick google search I couldn't really find anything, are people really claiming this?