The olive drab introduced in April 1944 was given the code SCC15 (standard camouflage colour). As Clive points out, though BS381 existed before the war, some codes and indeed colours of a particular code have changed over the years. I always understood that SCC15 became BS298 without change but I do not know for sure.
My Sherman colour looks different now than when I painted it in 2004, 65 years plus will have a large effect!
If you like the colour and it's close enough......