We're lucky in that CIE/IR struggled until quite late on to put out a consistent shade of orange. We get away with these off-shades and in fact a uniform shade of orange in a train, even of mk3's, looks wrong. We can mix and match the new MM mk2ds and the earlier (later!) ones, as well as the MM mk2a/b's and the upcoming IRM mk2c's and they will look spot on.