I was just looking at the " Friendly Boxing Match" set I bought a few weeks ago. While the US boxer's skin tone is white on the cover oddly the Valejo/ Life Color paint chart, on the back calls for brown skin tone. Then there is the obvious black facial; features.
I suppose the paratroops could have got a black GI from food services or transportation or other all black unit with a known pro boxing background to teach the Brits a lesson.. Joe Lewis often fought exhibition match for US troops but in a regulation ring for hundreds; not six or seven troops on the edge of a runway.
More likely who ever designed the figures was unaware sorry history of segregation in the US military during World War Two. MB tried to correct the mistake with the cover art.