West Indian servicemen (and women) in the UK were known to have a hard time from US servicemen (and from the British too, but to a notably lesser extent).
From
Race, Empire and British Wartime National Identity, 1939-1945
As early as June 1942 (the first troops arrived in the late winter of 1941-2) the Colonial Office began hearing complaints about how white Americans treated black Britons. The presence of the Americans in any Service hostel made it impossible for colonial servicemen to enter.
Colonial officials anxiously discussed the matter during the summer of 1942. Although John L. Keith of the welfare division wished to inform the Americans of the attitude of tolerance and non-discrimination that he claimed the Colonial Office was trying to foster, his colleagues warned him that it would cause enormous resentment if the British attempted to `educate' the Americans on the matter.
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Incidents of racial discrimination against black Britons either by or in connection with the presence of American troops persisted throughout the war. Beginning in the autumn of 1942 the welfare officers of the Ministry of Labour found themselves preoccupied with the issue.
By January 1943, Learie Constantine was reporting a steady deterioration in the relationship of white Americans to `our own Colonial People'. Constantine was himself subject to abuse by an American when he was eating in a restaurant with a white female colleague from the Ministry of Labour. By the summer of 1944 Arnold Watson had become increasingly frustrated that nothing positive was being done to stop the discrimination that West Indians were facing in the Liverpool area.
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Generally, wherever black British subjects encountered white Americans they faced Jim Crow tactics.
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The most celebrated involved Learie Constantine, who was denied a room at the Bedford Hotel in London on the grounds of race by a manager who claimed that the presence of blacks bothered American officers staying at the hotel.