"I was under the impression reinforcements were sent wherever needed regardless of race and the men where to busy to stay alive to worry about the colour of their skin"The men may well have been but institutional racism ran deep in the US Armed Forces and the US in general. During WW2, where arguably the manpower need was much greater, black marines were assigned to combat support functions, engineering and construction work for the most part. The Marines were among the most resistant of the services to racial integration and that goes all the way back through their history. It's a sad story actually.
As I said things started to change under Truman but the executive order requiring desegregation had only come into effect in 1948 and the USMC seems to have been very slow in implementing it, as they had been with an earlier order under Roosevelt. Were there black marines who fought in Korea? Yes but in small numbers. At the outbreak of the war, they represented about four percent of the USMC's total strength and that rose to about six percent by the end of the war. For the first half of the war it would not be uncommon for there to be one black marine to a whole company.
If you are interested, you'll find quite a bit of interest here:
https://www.marines.mil/Portals/1/Publications/Blacks%20in%20the%20Marine%20Corps%20%20PCN%2019000306200_3.pdfEven the USMC admits some of its failings and to be fair the institutional malaise and awful treatment meted out to many African Americans was paralleled in the US Army, which still had all white and all black units in Korea, despite desegregation being official policy. There were also the vile examples of racism like the desertion/AWOL charges filed against members of the all black 24th Infantry in 1950.
It was somewhat different with Asian and Hispanic Americans, they tended to be integrated in combat arms.
It's good you've included some black marines, hopefully it's a talking point for games.