[julie_m]

I would assume it was a production change; it might indicate whether the machine had the early ROM or the later one, or maybe the red paint just got too expensive. Or maybe the case supplied in the kit of parts to build at home had all-black raised lettering. (My own one was bought ready-made, and had the red lettering ..... Not sure which ROM it had.)

Be nice to know the real reason, though .....